board/jse/flash.c: fix GCC 4.6 build warnings

Fix:
flash.c: In function 'flash_erase':
flash.c:304:24: warning: variable 'l_sect' set but not used
[-Wunused-but-set-variable]

In addition, remove some dead code.

Signed-off-by: Wolfgang Denk <wd@denx.de>