ARM: 5991/1: Fix regression in restore_user_regs macro

ARMv5T and earlier require that a ldm {}^ instruction is not followed
by an instruction that accesses banked registers. This patch restores
the nop that was lost in commit b86040a5.

Signed-off-by: Anders Grafström <grfstrm@users.sourceforge.net>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>