drm/amdgpu: Fix the null pointer when load rlc firmware

If the RLC firmware is invalid because of wrong header size,
the pointer to the rlc firmware is released in function
amdgpu_ucode_request. There will be a null pointer error
in subsequent use. So skip validation to fix it.

Signed-off-by: Ma Jun <Jun.Ma2@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>