Merge change from upstream linux kernel submitted by OpenBSD:

drm/radeon: fix-up some float to fixed conversion thinkos

Spotted by Brad Smith when porting to OpenBSD.
Noticed-by: Brad Smith <brad@comstyle.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

ref: https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=1cd73ff7

Remove #ifdef DUMBBELL_WIP in favor of upstream fix.

Phabric:	https://phabric.freebsd.org/D423
Reviewed by:	dumbbell, jkim
MFC after:	2 weeks