flash: fix FC_FLEX_RAM class code path

If the flash class was defined as FC_FLEX_RAM then this would always drop
through to the default handler.

This bug was found by clang, so untested.

Change-Id: I2d9fe6415dd216728a145519400f7b9ef1bd3c3a
Signed-off-by: Spencer Oliver <spen@spen-soft.co.uk>
Reviewed-on: http://openocd.zylin.com/773


Tested-by: jenkins
Reviewed-by: Freddie Chopin <freddie.chopin@gmail.com>
Reviewed-by: Mathias Küster <kesmtp@freenet.de>