input: omap: void using mach/*.h headers

The omap-keypad driver currently relies on including mach/memory.h
implicitly, but that won't happen once omap1 is converted to
CONFIG_ARCH_MULTIPLATFORM. Include the required header
explicitly.

Acked-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>