gfs2: Cosmetic gfs2_dinode_{in,out} cleanup

commit 7db35444 upstream.

In each of the two functions, add an inode variable that points to
&ip->i_inode and use that throughout the rest of the function.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>