[JFFS2] Fix writebuffer recovery in the first page of a block

For the case when nand_write_page fail with -EIO for the first page in an
eraseblock, jffs2_wbuf_recover ends up producing a BUG in jffs2_block_refile
as jeb->first_node is not yet set up (it's set up later in jffs2_wbuf_recover).
This BUG is not really a bug; it's just jffs2_wbuf_recover calling
jffs2_block_refile with the wrong second parameter.
This patch takes care of this situation.

Signed-off-by: Vitaly Wool <vwool@ru.mvista.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>