netfs: fix parameter of cleanup()

The order of these two parameters is just reversed. gcc didn't warn on
that, probably because 'void *' can be converted from or to other
pointer types without warning.

Cc: stable@vger.kernel.org
Fixes: 3d3c9504 ("netfs: Provide readahead and readpage netfs helpers")
Fixes: e1b1240c ("netfs: Add write_begin helper")
Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Link: https://lore.kernel.org/r/20211207031449.100510-1-jefflexu@linux.alibaba.com/ # v1