drm: remove redundant code form drm_ioc32.c

The compat ioctl handler ends up calling access_ok() twice: first
indirectly inside compat_alloc_user_space() and then after returning
from that function. This patch fixes issue.

v2: there were three invalid removals of access_ok() that I've fixed.
Also went through all the changes couple of times and verified that
access_ok() is only removed when the buffer is allocated with
compat_alloc_user_space(). My deepest apologies for this kind of
sloppiness!

Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>