board/rbc823/flash.c: Fix flash initalization

board/rbc823/flash.c: Fix flash initalization

The RBC823 has only one NOR flash bank.  Remove all code trying to
deal with a second bank.  This also fixes a number of GCC 4.6 build
warnings:
flash.c: In function 'flash_init':
flash.c:62:12: warning: array subscript is above array bounds
[-Warray-bounds]
flash.c:63:12: warning: array subscript is above array bounds
[-Warray-bounds]
flash.c:66:12: warning: array subscript is above array bounds
[-Warray-bounds]

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