mtd: rawnand: omap_gpmc: Fix build warning on 64-bit platforms

mtd: rawnand: omap_gpmc: Fix build warning on 64-bit platforms

Pointer size cannot be assumed to be 32-bit, so use
use uintptr_t instead of uint32_t.

Fixes the below build warning on 64-bit builds.

drivers/mtd/nand/raw/omap_gpmc.c:439:10: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
  head = ((uint32_t) buf) % 4;

Signed-off-by: Roger Quadros <rogerq@kernel.org>
Reviewed-by: Michael Trimarchi <michael@amarulasolutions.com>
Link: https://lore.kernel.org/all/20221011115012.6181-4-rogerq@kernel.org
Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>