media: ipu3-imgu: Fix compiler warnings

Address a few false positive compiler warnings related to uninitialised
variables. While at it, use bool where bool is needed and %u to print an
unsigned integer.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>