mtd: lpddr_cmds: make function static

do_xxlock() is only used locally. This silences a sparse warning:

drivers/mtd/lpddr/lpddr_cmds.c:706:5: warning: no previous prototype for 'do_xxlock' [-Wmissing-prototypes]

Signed-off-by: Brian Norris <computersforpeace@gmail.com>

drivers/mtd/lpddr/lpddr_cmds.c

@@ -703,7 +703,7 @@ static int lpddr_erase(struct mtd_info *mtd, struct erase_info *instr)
 
 #define DO_XXLOCK_LOCK		1
 #define DO_XXLOCK_UNLOCK	2
-int do_xxlock(struct mtd_info *mtd, loff_t adr, uint32_t len, int thunk)
+static int do_xxlock(struct mtd_info *mtd, loff_t adr, uint32_t len, int thunk)
 {
 	int ret = 0;
 	struct map_info *map = mtd->priv;