Most error branches following the call to pmcraid_get_free_cmd contain a
call to pmcraid_return_cmd. This patch add these calls where they are
missing.

Moreover, most error branches following the call to class_create contain
a call to class_destroy. This patch add these calls where they are
missing.

This issue was found with Hector.
Signed-off-by: Quentin Lambert <lambert.quentin@gmail.com>
Reviewed-by: Tomas Henzl <thenzl@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>