media: imx274: Silence uninitialized variable warning

Smatch complains that "err" can be uninitialized if we have a zero size
write.  The flow analysis is a little complicated so I'm not sure if
that's possible or not, but it's harmless to set this to zero and it
makes the code easier to read.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>