drm/amdgpu/powerplay: fix spelling mistake "unsuported" -> "unsupported"

There is a spelling mistake in a pr_err error message. Fix it. Also
add a space after a comma to clean up a checkpatch warning.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>