flash/nor/stm32f2x: fix erase on STM32F413/423

flash/nor/stm32f2x: fix erase on STM32F413/423

Theese devices do not have a gap in sector numbering.
The driver translates sectors numbers 12 13... to 16 17... as used on dual
bank flash devices. Therefore erase of sector 12 and above fails with error
	'stm32x device protected'
on F413/423.

Drop sector number translation for devices without has_large_mem flag.

Change-Id: I65531c0dfe02e2fd0f3d68f0615e0926e9901391
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-on: http://openocd.zylin.com/4299
Tested-by: jenkins
Reviewed-by: Andreas Bolsch <hyphen0break@gmail.com>
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>