ARC: unbork 5.11 bootup: fix snafu in _TIF_NOTIFY_SIGNAL handling

Linux 5.11.rcX was failing to boot on ARC HSDK board. Turns out we have
a couple of issues, this being the first one, and I'm to blame as I
didn't pay attention during review.

TIF_NOTIFY_SIGNAL support requires checking multiple TIF_* bits in
kernel return code path. Old code only needed to check a single bit so
BBIT0 <TIF_SIGPENDING> worked. New code needs to check multiple bits so
AND <bit-mask> instruction. So needs to use bit mask variant _TIF_SIGPENDING

Cc: Jens Axboe <axboe@kernel.dk>
Fixes: 53855e12 ("arc: add support for TIF_NOTIFY_SIGNAL")
Link: https://github.com/foss-for-synopsys-dwc-arc-processors/linux/issues/34


Signed-off-by: Vineet Gupta <vgupta@synopsys.com>