fetch-pack: directly end negotiation if ACK ready

fetch-pack: directly end negotiation if ACK ready

When "ACK %s ready" is received, find_common() clears rev_list in an
attempt to stop further "have" lines from being sent [1]. It is much
more readable to explicitly break from the loop instead.

So explicitly break from the loop, and make the clearing of the rev_list
happen unconditionally.

[1] The rationale is further described in the originating commit
f2cba9299b ("fetch-pack: Finish negotation if remote replies "ACK %s
ready"", 2011-03-14).

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>