davinci: sram warning fix

CC      arch/arm/mach-davinci/sram.o
arch/arm/mach-davinci/sram.c: In function 'sram_init':
arch/arm/mach-davinci/sram.c:63: warning: comparison of distinct pointer types lacks a cast

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>