amdgpu/amdgpu_psp: remove unneeded ret variable

Return value from amdgpu_bo_create_kernel() directly instead
of taking this in another redundant variable.

Reported-by: Zeal Robot <zealci@zte.com.cn>
Signed-off-by: Minghao Chi <chi.minghao@zte.com.cn>
Signed-off-by: CGEL ZTE <cgel.zte@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>