[GFS2] Fix cast from unsigned int to s64

This fixes bz 444829 where allocating a new block caused gfs2 file systems to
report 0 bytes used in df. It was caused by a broken cast from an unsigned int
in gfs2_block_alloc() to a negative s64 in gfs2_statfs_change(). This patch
casts the unsigned int to an s64 before the unary minus is applied.
Signed-off-by: NAndrew Price <andy@andrewprice.me.uk>
Signed-off-by: NSteven Whitehouse <swhiteho@redhat.com>

fs/gfs2/rgrp.c

@@ -1495,7 +1495,7 @@ u64 gfs2_alloc_block(struct gfs2_inode *ip, unsigned int *n)
 
 	al->al_alloced += *n;
 
-	gfs2_statfs_change(sdp, 0, -*n, 0);
+	gfs2_statfs_change(sdp, 0, -(s64)*n, 0);
 	gfs2_quota_change(ip, *n, ip->i_inode.i_uid, ip->i_inode.i_gid);
 
 	spin_lock(&sdp->sd_rindex_spin);