drm/amdgpu: Remove unnecessary return value check

There is no need to check return value, as the function internally
used - amdgpu_discovery_read_binary_from_vram() - returns void.

Signed-off-by: Lijo Lazar <lijo.lazar@amd.com>
Reviewed-by: Le Ma <le.ma@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>