[PATCH] jffs2: memory leak in jffs2_scan_medium()

If jffs2_scan_eraseblock() fails and the exit path is taken, 's' is not
being deallocated.

Reported by Coverity, CID: 1258.

Signed-off-by: Florin Malita <fmalita@gmail.com>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>