media: vpss: fix a potential NULL pointer dereference

In case ioremap fails, the fix returns -ENOMEM to avoid NULL
pointer dereference.

Signed-off-by: Kangjie Lu <kjlu@umn.edu>
Acked-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Reviewed-by: Mukesh Ojha <mojha@codeaurora.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>