mtd: rawnand: nand_spl_loaders: Fix cast type build warning

mtd: rawnand: nand_spl_loaders: Fix cast type build warning

Fixes the below build warning on 64-bit platforms.

drivers/mtd/nand/raw/nand_spl_loaders.c:26:21: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
      dst = (void *)((int)dst - page_offset);

Signed-off-by: Roger Quadros <rogerq@kernel.org>
Reviewed-by: Michael Trimarchi <michael@amarulasolutions.com>
Link: https://lore.kernel.org/all/20221011115012.6181-8-rogerq@kernel.org
Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>