Fix missing __iomem attribute. This fixes the sparse warning:

  CHECK   arch/arm/mach-davinci/sram.c
arch/arm/mach-davinci/sram.c:75:8: warning: incorrect type in assignment (different address spaces)
arch/arm/mach-davinci/sram.c:75:8:    expected void *addr
arch/arm/mach-davinci/sram.c:75:8:    got void [noderef] <asn:2>*
arch/arm/mach-davinci/sram.c:81:12: warning: incorrect type in argument 1 (different address spaces)
arch/arm/mach-davinci/sram.c:81:12:    expected void volatile [noderef] <asn:2>*addr
arch/arm/mach-davinci/sram.c:81:12:    got void *addr
Signed-off-by: Sekhar Nori <nsekhar@ti.com>