memory: of: Remove unneeded extern from function declarations

Function declarations in headers do not need to come with extern
keyword.  Remove them to make the declaration slightly shorter.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>

drivers/memory/of_memory.h

@@ -3,21 +3,22 @@
  * OpenFirmware helpers for memory drivers
  *
  * Copyright (C) 2012 Texas Instruments, Inc.
+ * Copyright (C) 2020 Krzysztof Kozlowski <krzk@kernel.org>
  */
 
 #ifndef __LINUX_MEMORY_OF_REG_H
 #define __LINUX_MEMORY_OF_REG_H
 
 #if defined(CONFIG_OF) && defined(CONFIG_DDR)
-extern const struct lpddr2_min_tck *of_get_min_tck(struct device_node *np,
+const struct lpddr2_min_tck *of_get_min_tck(struct device_node *np,
 					    struct device *dev);
-extern const struct lpddr2_timings
-	*of_get_ddr_timings(struct device_node *np_ddr, struct device *dev,
+const struct lpddr2_timings *of_get_ddr_timings(struct device_node *np_ddr,
+						struct device *dev,
 						u32 device_type, u32 *nr_frequencies);
-extern const struct lpddr3_min_tck
-	*of_lpddr3_get_min_tck(struct device_node *np, struct device *dev);
-extern const struct lpddr3_timings
-	*of_lpddr3_get_ddr_timings(struct device_node *np_ddr,
+const struct lpddr3_min_tck *of_lpddr3_get_min_tck(struct device_node *np,
+						   struct device *dev);
+const struct lpddr3_timings *
+of_lpddr3_get_ddr_timings(struct device_node *np_ddr,
 			  struct device *dev, u32 device_type, u32 *nr_frequencies);
 #else
 static inline const struct lpddr2_min_tck