gfs2: Fix an incorrect gfs2_assert()

When updating the inode information after a change in allocation,
convert the change into the same units as the inode's i_blocks count
before comparing it in an assertion.

Also, change the comparison so that it is still possible to set i_blocks
to zero by adding -i_blocks, something that was previously only possible
because of the difference in units.
Signed-off-by: Tim Smith <tim.smith@citrix.com>
Signed-off-by: Bob Peterson <rpeterso@redhat.com>

fs/gfs2/inode.h

@@ -59,8 +59,8 @@ static inline u64 gfs2_get_inode_blocks(const struct inode *inode)
 
 static inline void gfs2_add_inode_blocks(struct inode *inode, s64 change)
 {
-	gfs2_assert(GFS2_SB(inode), (change >= 0 || inode->i_blocks > -change));
-	change *= (GFS2_SB(inode)->sd_sb.sb_bsize/GFS2_BASIC_BLOCK);
+	change <<= inode->i_blkbits - GFS2_BASIC_BLOCK_SHIFT;
+	gfs2_assert(GFS2_SB(inode), (change >= 0 || inode->i_blocks >= -change));
 	inode->i_blocks += change;
 }