jfs: fix GPF in diFree

Avoid passing inode with
JFS_SBI(inode->i_sb)->ipimap == NULL to
diFree()[1]. GFP will appear:

	struct inode *ipimap = JFS_SBI(ip->i_sb)->ipimap;
	struct inomap *imap = JFS_IP(ipimap)->i_imap;

JFS_IP() will return invalid pointer when ipimap == NULL

Call Trace:
 diFree+0x13d/0x2dc0 fs/jfs/jfs_imap.c:853 [1]
 jfs_evict_inode+0x2c9/0x370 fs/jfs/inode.c:154
 evict+0x2ed/0x750 fs/inode.c:578
 iput_final fs/inode.c:1654 [inline]
 iput.part.0+0x3fe/0x820 fs/inode.c:1680
 iput+0x58/0x70 fs/inode.c:1670

Reported-and-tested-by: syzbot+0a89a7b56db04c21a656@syzkaller.appspotmail.com
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>

fs/jfs/inode.c

@@ -151,7 +151,8 @@ void jfs_evict_inode(struct inode *inode)
 			if (test_cflag(COMMIT_Freewmap, inode))
 				jfs_free_zero_link(inode);
 
-			diFree(inode);
+			if (JFS_SBI(inode->i_sb)->ipimap)
+				diFree(inode);
 
 			/*
 			 * Free the inode from the quota allocation.