media: allegro: Fix some NULL vs IS_ERR() checks in probe

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

Fixes: f20387df ("media: allegro: add Allegro DVT video IP core driver")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>