mtd: maps: cfi_flagadm: add missing __iomem annotation

Added missing __iomem annotation and staticized local symbols
in order to fix the following sparse warnings:

drivers/mtd/maps/cfi_flagadm.c:58:17: warning: symbol 'flagadm_map' was not declared. Should it be static?
drivers/mtd/maps/cfi_flagadm.c:64:22: warning: symbol 'flagadm_parts' was not declared. Should it be static?
drivers/mtd/maps/cfi_flagadm.c:115:18: warning: cast removes address space of expression
drivers/mtd/maps/cfi_flagadm.c:115:18: warning: incorrect type in argument 1 (different address spaces)
drivers/mtd/maps/cfi_flagadm.c:115:18:    expected void volatile [noderef] <asn:2>*addr
drivers/mtd/maps/cfi_flagadm.c:115:18:    got void *<noident>
drivers/mtd/maps/cfi_flagadm.c:126:26: warning: cast removes address space of expression
drivers/mtd/maps/cfi_flagadm.c:126:26: warning: incorrect type in argument 1 (different address spaces)
drivers/mtd/maps/cfi_flagadm.c:126:26:    expected void volatile [noderef] <asn:2>*addr
drivers/mtd/maps/cfi_flagadm.c:126:26:    got void *<noident>
drivers/mtd/maps/cfi_flagadm.c:127:36: warning: Using plain integer as NULL pointer

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>