archiver.bbclass: Fix tar name for git repositories
When archiving the original source, the git repositories have the name as
they are in the $DL_DIR plus the source revision; i.e.
"git.yoctoproject.org.linux-yocto-4.4.git.89419d8b90_dadb436904.tar.gz".
This change set the tar name to $PF.tar.gz instead, to have consistency with
the others archives created by the class.
Signed-off-by: Mariano Lopez <mariano.lopez@linux.intel.com> Signed-off-by: Ross Burton <ross.burton@intel.com>
