drm/amd/amdgpu: Fix flow control in uvd_v4_2_stop()

Break out of outer loop properly.

Signed-off-by: Tom St Denis <tom.stdenis@amd.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>