queue: enter if CQ needs it, even if SQ doesn't
queue: enter if CQ needs it, even if SQ doesn't

Even when not submitting SQEs, io_uring_enter()
may be needed for IOPOLL mode or if the CQ overflowed.
Let io_uring_submit() still make the syscall in this case.

Fixes: 504efe18c213 ("queue: avoid io_uring_enter() with no SQEs")
Signed-off-by: Caleb Sander <fa2ca9518879ab9dbdedcf10ba3b1999589f7d8b@purestorage.com>

axboe/liburing,axboe/liburing,axboe/liburing