[MTD] [NOR] Fix incorrect interface code for x16/x32 chips

According to "Common Flash Memory Interface Publication 100" dated December 1,
2001, the interface code for x16/x32 chips is 0x0005, and not 0x0004 used so
far.

Signed-off-by: Bartlomiej Sieka <tur@semihalf.com>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>