Recently the __copy_tofrom_user routine was modified to avoid doing
prefetches past the end of the source array.  However, in doing so we
introduced a bug in that it now returns the wrong value for the number
of bytes not copied when a fault is encountered.  This fixes it to
return the correct number.
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>