x86: Use correct byte-sized register constraint in __add()

x86: Use correct byte-sized register constraint in __add()

commit 8c91c5325e107ec17e40a59a47c6517387d64eb7 upstream.

Similar to:

 2ca052a x86: Use correct byte-sized register constraint in __xchg_op()

... the __add() macro also needs to use a "q" constraint in the
byte-sized case, lest we try to generate an illegal register.

Link: http://lkml.kernel.org/r/4F7A3315.501@goop.org
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Leigh Scott <leigh123linux@googlemail.com>
Cc: Thomas Reitmayr <treitmayr@devbase.at>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>