[JFFS2] Remove forgotten summary code

Remove forgotten lines from jffs2_scan_eraseblock() which
were unnecessary and may cause problem in some environments.

Thanks to Alexander Belyakov <alexander.belyakov@intel.com>.

Signed-off-by: Ferenc Havasi <havasi@inf.u-szeged.hu>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>