drm/radeon: fix possible segfault when parsing pm tables

If we have a empty power table, bail early and allocate
the default power state.

Should fix:
https://bugs.freedesktop.org/show_bug.cgi?id=63865

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
1 file changed