x86: copy_from_user() should not return -EFAULT

Callers of copy_from_user() expect it to return the number of bytes
it could not copy. In no case it is supposed to return -EFAULT.

In case of a detected buffer overflow just return the requested
length. In addition one could think of a memset that would clear
the size of the target object.

[ hpa: code is not in .32 so not needed for -stable ]

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Acked-by: Arjan van de Ven <arjan@linux.intel.com>
LKML-Reference: <20100105131911.GC5480@osiris.boeblingen.de.ibm.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>