ARM: 8917/1: mm: include <asm/set_memory.h>

The definitions of set_kernel_text_rw() and
set_kernel_text_ro() are in <asm/set_memory.h>
but this is not included in init.c which defines
these. Silence the following warnings by including
the <asm/set_memory.h> header.

arch/arm/mm/init.c:669:6: warning: symbol 'set_kernel_text_rw' was not declared. Should it be static?
arch/arm/mm/init.c:678:6: warning: symbol 'set_kernel_text_ro' was not declared. Should it be static?

Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>