when last==first==0 then mass erase is executed, it's faster.
the page marking was wrong in this case.
Change-Id: I5c579d59b5c4778cf057cb5986e086abdd4209b2
Signed-off-by: Rodrigo L. Rosa <rodrigorosa.lg@gmail.com>
Reviewed-on: http://openocd.zylin.com/232
Tested-by: jenkins
Reviewed-by: Øyvind Harboe <oyvindharboe@gmail.com>