Use WARN_ON() inside if-condition when possible.

v2: Squash in coding style fix (Alex)
Signed-off-by: NNirmoy Das <nirmoy.das@amd.com>
Reviewed-by: NAlex Deucher <alexander.deucher@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>