libceph: drop ->monmap and err initialization

Call to build_initial_monmap() is one stone two birds.  Explicitly it
initializes err variable. Implicitly it initializes ->monmap via call to
kzalloc().  We should only declare err and ->monmap is taken care of by
ceph_monc_init() prototype.

Signed-off-by: Jean Sacren <sakiwit@gmail.com>
Reviewed-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>