GPU-DRM: Delete unnecessary checks before drm_property_unreference_blob()

The drm_property_unreference_blob() function tests whether its argument
is NULL and then returns immediately.
Thus the tests around the calls are not needed.

This issue was detected by using the Coccinelle software.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Link: http://patchwork.freedesktop.org/patch/msgid/563C8B3E.405@users.sourceforge.net


Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>