habanalabs: check the return value of hl_cs_poll_fences()

As part of handling of the multi-CS wait ioctl, hl_cs_poll_fences() is
called in a "while (true)" loop. This function can fail, but the
checking of its return value was missed.
Add this check and exit the loop in case of a failure.

Signed-off-by: Tomer Tayar <ttayar@habana.ai>
Reviewed-by: Oded Gabbay <ogabbay@kernel.org>
Signed-off-by: Oded Gabbay <ogabbay@kernel.org>