BugLink: http://bugs.launchpad.net/bugs/1546572

In case CONFIG_DRM_AMD_POWERPLAY is defined and amdgpu.powerplay=0.
some functions in powrplay can also be called by DAL. and the input parameter is *adev.
if just check point not NULL was not enough and will lead to NULL point error.

V2: AGD: rebase on upstream
Signed-off-by: Rex Zhu <Rex.Zhu@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit a969e163)
Signed-off-by: Alberto Milone <alberto.milone@canonical.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>