kunit: fix uninitialized variables bug in attributes filtering

Fix smatch warnings regarding uninitialized variables in the filtering
patch of the new KUnit Attributes feature.

Fixes: 529534e8

 ("kunit: Add ability to filter attributes")

Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/r/202307270610.s0w4NKEn-lkp@intel.com/

Signed-off-by: Rae Moar <rmoar@google.com>
Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>