git p4 doc: use two-line style for options with multiple spellings

Thomas Rast noticed the docs have a mix of styles when
it comes to options with multiple spellings.  Standardize
the couple in git-p4.txt that are odd.

Instead of:
  -n, --dry-run::

Do this:
  -n::
  --dry-run::

See
http://thread.gmane.org/gmane.comp.version-control.git/219936/focus=219945

Signed-off-by: Pete Wyckoff <pw@padd.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-p4.txt

@@ -168,7 +168,8 @@ All commands except clone accept these options.
 --git-dir <dir>::
 	Set the 'GIT_DIR' environment variable.  See linkgit:git[1].
 
---verbose, -v::
+-v::
+--verbose::
 	Provide more progress information.
 
 Sync options
@@ -279,7 +280,8 @@ These options can be used to modify 'git p4 submit' behavior.
 	Export tags from Git as p4 labels. Tags found in Git are applied
 	to the perforce working directory.
 
---dry-run, -n::
+-n::
+--dry-run::
 	Show just what commits would be submitted to p4; do not change
 	state in Git or p4.