poll_wait: kill the obsolete wait_address check

poll_wait: kill the obsolete wait_address check

This check is historical and no longer needed, wait_address is never NULL.
These days we rely on the poll_table->_qproc check. NULL if select/poll
is not going to sleep, or it already has a data to report, or all waiters
have already been registered after the 1st iteration.

However, poll_table *p can be NULL, see p9_fd_poll() for example, so we
can't remove the "p != NULL" check.

Link: https://lore.kernel.org/all/20250106180325.GF7233@redhat.com/
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Link: https://lore.kernel.org/r/20250107162724.GA18926@redhat.com
Signed-off-by: Christian Brauner <brauner@kernel.org>