drm/radeon: Fix sparc regression in r300_scratch()

Commit b4fe9454 ("drm/radeon: Fix
memory allocation failures in the preKMS command stream checking.")
added a regression in that it completely tossed the get_unaligned()
done by r300_scratch() which we added in commit
958a6f8c ("drm: radeon: Fix unaligned
access in r300_scratch().").

Put it back.

Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Matt Turner <mattst88@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>