[ARM] 3271/1: ARM EABI: fix calling of cmpxchg syscall emulation

Patch from Nicolas Pitre

This is kernel provided user space code.

Since a syscall is used, it has to be updated to work with EABI.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>