mtd: spi-nor: aspeed: set 4B setting for all chips

The driver made the wrong assumption that the 4B setting was
autodetected for all chips of the AST2500 FMC flash controller. This
is only the case for the CS0.

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Cyrille Pitchen <cyrille.pitchen@wedev4u.fr>