UBIFS: improve inode dumping function

Teach 'dbg_dump_inode()' dump directory entries for directory inodes.
This requires few additional changes:
1. The 'c' argument of 'dbg_dump_inode()' cannot be const any more.
2. Users of 'dbg_dump_inode()' should not have 'tnc_mutex' locked.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
diff --git a/fs/ubifs/tnc.c b/fs/ubifs/tnc.c
index 91b4213..48b6ee6 100644
--- a/fs/ubifs/tnc.c
+++ b/fs/ubifs/tnc.c
@@ -3337,9 +3337,10 @@
 	ubifs_err("inode %lu has size %lld, but there are data at offset %lld "
 		  "(data key %s)", (unsigned long)inode->i_ino, size,
 		  ((loff_t)block) << UBIFS_BLOCK_SHIFT, DBGKEY(key));
+	mutex_unlock(&c->tnc_mutex);
 	dbg_dump_inode(c, inode);
 	dbg_dump_stack();
-	err = -EINVAL;
+	return -EINVAL;
 
 out_unlock:
 	mutex_unlock(&c->tnc_mutex);