ppc32: fix copy_from_user()

[ Upstream commit 224264657b8b228f949b42346e09ed8c90136a8e ]

should clear on access_ok() failures.  Also remove the useless
range truncation logics.

Cc: stable@vger.kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>