finish_connect(): thinkofix

finish_connect(): thinkofix

All but one callers have ignore the return value from this
function, but the only caller, builtin-tar-tree.c::remote_tar(),
assumed it returns non-zero on failure and zero on success.  The
implementation however was returning either the waited pid
(which must be the same as its input) or -1 (an error).

Fix this thinko, while getting rid of an assignment of return
value from waitpid() into a variable of type int.

Signed-off-by: Junio C Hamano <junkio@cox.net>