alpha: Fix mixed up args in EXC macro in futex operations

Fix the typo (mixed up arguments) in the EXC macro in the futex
definitions introduced by commit ca282f69 (alpha: add a
helper for emitting exception table entries).

Cc: stable@vger.kernel.org      # v4.12+
Signed-off-by: Michael Cree <mcree@orcon.net.nz>
Signed-off-by: Matt Turner <mattst88@gmail.com>