MIPS: Audit: Fix hang in entry.S.

_TIF_WORK_MASK false had _TIF_SYSCALL_AUDIT set.  If a thread's
_TIF_SYSCALL_AUDIT is ever set this will lead to an endless loop on the
way out from a syscall.

Currently this is only a theoretic bug as init/Kconfig doesn't allow
AUDIT_SYSCALL to be enabled for MIPS.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>