drm/amdkfd: Don't create BUG due to incorrect user parameter

This patch changes a BUG_ON() statement to pr_debug, in case the user tries to
update a non-existing queue.

Signed-off-by: Oded Gabbay <oded.gabbay@amd.com>
Reviewed-by: Ben Goz <ben.goz@amd.com>
Reviewed-by: Jammy Zhou <Jammy.Zhou@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>