zvol: Fix suspend lock leaks (#16270)

In several functions, we use a flag variable to track whether
zv_suspend_lock is held. This flag was not getting reset in a
particular case where we need to retry the underlying operation,
resulting in a lock leak. Make sure to update the flag where necessary.

Signed-off-by: Mark Johnston <markj@FreeBSD.org>
Reviewed-by: Allan Jude <allan@klarasystems.com>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Tino Reichardt <milky-zfs@mcmilk.de>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>