git-p4: correct --prepare-p4-only instructions
git-p4: correct --prepare-p4-only instructions

If you use git-p4 with the "--prepare-p4-only" option, then
it prints the p4 command line to use. However, the command
line was incorrect: the changelist specification must be
supplied on standard input, not as an argument to p4.

Signed-off-by: Luke Diamand <6b3799be4300e44489a08090123f3842e6419da5@diamand.org>
Acked-by: Pete Wyckoff <1a91d62f7ca67399625a4368a6ab5d4a3baa6073@padd.com>
Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git