GCC with W=2 level of kernel compiler warnings warns about the use of
uninitialised variables in a few locations. While these uninitialised
variables were not used in reality, this still produced compiler warnings.

Address this by assigning the variables to NULL and checking for NULL in
places it is not expected, returning -EIO in that case. This provides
at least some sanity checking at runtime as the compiler appears unable to
do that at compile time.
Reported-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>