microblaze: bury sys_rt_sigsuspend_wrapper in nommu case too

It's been a dead code since commit 571202f5
Author: Michal Simek <monstr@monstr.eu>
Date:   Fri Dec 11 12:54:04 2009 +0100

    microblaze: Remove rt_sigsuspend wrapper

    Generic rt_sigsuspend syscalls doesn't need any asm wrapper.

but that commit has only removed it from entry.S, missing one in entry-nommu.S.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>