drm/radeon/DCE4+: clear bios scratch dpms bit (v2)

The BlankCrtc table in some DCE8 boards has some
logic shortcuts for the vbios when this bit is set.
Clear it for driver use.

v2: fix typo

Bug:
https://bugs.freedesktop.org/show_bug.cgi?id=73420



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