afs: Fix double inc of vnode->cb_break

afs: Fix double inc of vnode->cb_break

When __afs_break_callback() clears the CB_PROMISED flag, it increments
vnode->cb_break to trigger a future refetch of the status and callback -
however it also calls afs_clear_permits(), which also increments
vnode->cb_break.

Fix this by removing the increment from afs_clear_permits().

Whilst we're at it, fix the conditional call to afs_put_permits() as the
function checks to see if the argument is NULL, so the check is redundant.

Fixes: be080a6f43c4 ("afs: Overhaul permit caching");
Signed-off-by: David Howells <dhowells@redhat.com>