afs: Don't put afs_call in afs_wait_for_call_to_complete()

Don't put the afs_call struct in afs_wait_for_call_to_complete() but rather
have the caller do it.  This will allow the caller to fish stuff out of the
afs_call struct rather than the afs_addr_cursor struct, thereby allowing a
subsequent patch to subsume it.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org