mmc: core: Re-use DEFINE_SHOW_ATTRIBUTE() macro

...instead of open coding file operations followed by custom ->open()
callbacks per each attribute.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Avri Altman <avri.altman@wdc.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/core/debugfs.c

@@ -196,18 +196,7 @@ static int mmc_ios_show(struct seq_file *s, void *data)
 
 	return 0;
 }
-
-static int mmc_ios_open(struct inode *inode, struct file *file)
-{
-	return single_open(file, mmc_ios_show, inode->i_private);
-}
-
-static const struct file_operations mmc_ios_fops = {
-	.open		= mmc_ios_open,
-	.read		= seq_read,
-	.llseek		= seq_lseek,
-	.release	= single_release,
-};
+DEFINE_SHOW_ATTRIBUTE(mmc_ios);
 
 static int mmc_clock_opt_get(void *data, u64 *val)
 {