media: cedrus: Fix a NULL vs IS_ERR() check

The devm_ioremap_resource() function doesn't return NULL pointers, it
returns error pointers.

Fixes: 50e76151 ("media: platform: Add Cedrus VPU decoder driver")

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>