xfs: eliminate some newly-reported gcc warnings

Ionut Gabriel Popescu <poyo_vl@yahoo.com> submitted a simple change
to eliminate some "may be used uninitialized" warnings when building
XFS.  The reported condition seems to be something that GCC did not
used to recognize or report.  The warnings were produced by:

    gcc version 4.5.0 20100604
    [gcc-4_5-branch revision 160292] (SUSE Linux)
Signed-off-by: Ionut Gabriel Popescu <poyo_vl@yahoo.com>
Signed-off-by: Alex Elder <aelder@sgi.com>

fs/xfs/xfs_alloc.c

@@ -675,7 +675,7 @@ xfs_alloc_ag_vextent_near(
 	xfs_agblock_t	gtbnoa;		/* aligned ... */
 	xfs_extlen_t	gtdiff;		/* difference to right side entry */
 	xfs_extlen_t	gtlen;		/* length of right side entry */
-	xfs_extlen_t	gtlena;		/* aligned ... */
+	xfs_extlen_t	gtlena = 0;	/* aligned ... */
 	xfs_agblock_t	gtnew;		/* useful start bno of right side */
 	int		error;		/* error code */
 	int		i;		/* result code, temporary */
@@ -684,7 +684,7 @@ xfs_alloc_ag_vextent_near(
 	xfs_agblock_t	ltbnoa;		/* aligned ... */
 	xfs_extlen_t	ltdiff;		/* difference to left side entry */
 	xfs_extlen_t	ltlen;		/* length of left side entry */
-	xfs_extlen_t	ltlena;		/* aligned ... */
+	xfs_extlen_t	ltlena = 0;	/* aligned ... */
 	xfs_agblock_t	ltnew;		/* useful start bno of left side */
 	xfs_extlen_t	rlen;		/* length of returned extent */
 #if defined(DEBUG) && defined(__KERNEL__)