mtd: map: add back asm/barrier.h inclusion

The mb() macro is used in this header:

In file included from include/linux/mtd/qinfo.h:5,
from include/linux/mtd/pfow.h:8,
from drivers/mtd/lpddr/lpddr_cmds.c:14:
include/linux/mtd/map.h: In function 'inline_map_write':
include/linux/mtd/map.h:428:9: error: implicit declaration of function 'mb' [-Wimplicit-function-declaration]

Fixes: 56eb7c13b97c ("mtd: map: Don't use "proxy" headers")
Signed-off-by: Arnd Bergmann <[e-mail]>
Acked-by: Andy Shevchenko <[e-mail]>
Signed-off-by: Miquel Raynal <[e-mail]>

include/linux/mtd/map.h

···
 #include <linux/string.h>
 #include <linux/types.h>
 #include <linux/unaligned.h>
+#include <asm/barrier.h>
 
 struct device_node;
 struct module;