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

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 <arnd@arndb.de>
Acked-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>