UBIFS: add missing ui pointer in debugging code

If UBIFS_DEBUG is defined an additional assertion of the ui_lock
spinlock in do_writepage cannot compile because the ui pointer has not
been previously declared.

Fix this by declaring and initializing the ui pointer in case
UBIFS_DEBUG is defined.
Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>

fs/ubifs/file.c

@@ -903,6 +903,7 @@ static int do_writepage(struct page *page, int len)
 	struct ubifs_info *c = inode->i_sb->s_fs_info;
 
 #ifdef UBIFS_DEBUG
+	struct ubifs_inode *ui = ubifs_inode(inode);
 	spin_lock(&ui->ui_lock);
 	ubifs_assert(page->index <= ui->synced_i_size << PAGE_CACHE_SIZE);
 	spin_unlock(&ui->ui_lock);