mips: copy_from_user() must zero the destination on access_ok() failure

[ Upstream commit e69d700535ac43a18032b3c399c69bf4639e89a2 ]

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