[IA64] Optimize ticket spinlocks in fsys_rt_sigprocmask

Tony's fix (f574c843

) has a small bug,
it incorrectly uses "r3" as a scratch register in the first of the two
unlock paths ... it is also inefficient.  Optimize the fast path again.

Signed-off-by: Petr Tesarik <ptesarik@suse.cz>
Signed-off-by: Tony Luck <tony.luck@intel.com>