dump.c: Fix memory leak issue in cleanup processing for dump_init()

In dump_init(), when failure occurs, need notice about 'fd' and memory
mapping. So call dump_cleanup() for it (need let all initializations at
front).

Also simplify dump_cleanup(): remove redundant 'ret' and redundant 'fd'
checking.

Signed-off-by: Chen Gang <gang.chen.5i5j@gmail.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>