flash: fix incorrect stm32f2x/stm32f4x flash size register

flash: fix incorrect stm32f2x/stm32f4x flash size register

The ref manuals for the stm32f2x (RM0033 Rev4) and stm32f4x (RM0090 rev1)
are unclear to the address of the flash size register (F_ID).

According to contacts @ ST this is the correct address, the manuals will be
updated in due coarse.

Change-Id: If9fb83b3100458d17038cf27c2b23355e1dc5a9e
Signed-off-by: Spencer Oliver <spen@spen-soft.co.uk>
Reviewed-on: http://openocd.zylin.com/448
Reviewed-by: Peter Stuge <peter@stuge.se>
Tested-by: jenkins