once: don't use a work queue to reset sleepable static key

Pointless overhead to use a work queue to reset the static key for a
DO_ONCE_SLEEPABLE() invocation.

Note that the previous code path included a BUG_ON() if the static key
was already disabled. Dropped that as part of this change because:
1) Use of BUG_ON() is highly discouraged.
2) There is a WARN_ON() in the static_branch_disable() code path
that would provide adequate breadcrumbs to debug any issue.

Link: https://lkml.kernel.org/r/aWU4tfTju1l3oZCu@agluck-desk3
Signed-off-by: Tony Luck <tony.luck@intel.com>
Reported-by: Reinette Chatre <reinette.chatre@intel.com>
Cc: Eric Dumazet <edumazet@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>