spi: struct spi_device constification

Merge series from Geert Uytterhoeven <geert+renesas@glider.be>:

After noticing new cases of casting away constness, I went over all
spi_get_*() functions and their callers, and made the following changes:
  1. Make all pointer parameters const where possible,
  2. Remove unneeded casts, some not even related to constness.

drivers/spi/spi-fsl-dspi.c

@@ -1068,7 +1068,7 @@ static int dspi_setup(struct spi_device *spi)
 
 static void dspi_cleanup(struct spi_device *spi)
 {
-	struct chip_data *chip = spi_get_ctldata((struct spi_device *)spi);
+	struct chip_data *chip = spi_get_ctldata(spi);
 
 	dev_dbg(&spi->dev, "spi_device %u.%u cleanup\n",
 		spi->controller->bus_num, spi_get_chipselect(spi, 0));

drivers/spi/spi-sh-msiof.c

@@ -587,11 +587,11 @@ static int sh_msiof_prepare_message(struct spi_controller *ctlr,
 	u32 ss, cs_high;
 
 	/* Configure pins before asserting CS */
-	if (spi_get_csgpiod((struct spi_device *)spi, 0)) {
+	if (spi_get_csgpiod(spi, 0)) {
 		ss = ctlr->unused_native_cs;
 		cs_high = p->native_cs_high;
 	} else {
-		ss = spi_get_chipselect((struct spi_device *)spi, 0);
+		ss = spi_get_chipselect(spi, 0);
 		cs_high = !!(spi->mode & SPI_CS_HIGH);
 	}
 	sh_msiof_spi_set_pin_regs(p, ss, !!(spi->mode & SPI_CPOL),

include/linux/spi/spi.h

@@ -244,7 +244,7 @@ static inline void spi_dev_put(struct spi_device *spi)
 }
 
 /* ctldata is for the bus_controller driver's runtime state */
-static inline void *spi_get_ctldata(struct spi_device *spi)
+static inline void *spi_get_ctldata(const struct spi_device *spi)
 {
 	return spi->controller_state;
 }
@@ -261,12 +261,12 @@ static inline void spi_set_drvdata(struct spi_device *spi, void *data)
 	dev_set_drvdata(&spi->dev, data);
 }
 
-static inline void *spi_get_drvdata(struct spi_device *spi)
+static inline void *spi_get_drvdata(const struct spi_device *spi)
 {
 	return dev_get_drvdata(&spi->dev);
 }
 
-static inline u8 spi_get_chipselect(struct spi_device *spi, u8 idx)
+static inline u8 spi_get_chipselect(const struct spi_device *spi, u8 idx)
 {
 	return spi->chip_select;
 }
@@ -276,7 +276,7 @@ static inline void spi_set_chipselect(struct spi_device *spi, u8 idx, u8 chipsel
 	spi->chip_select = chipselect;
 }
 
-static inline struct gpio_desc *spi_get_csgpiod(struct spi_device *spi, u8 idx)
+static inline struct gpio_desc *spi_get_csgpiod(const struct spi_device *spi, u8 idx)
 {
 	return spi->cs_gpiod;
 }