[MTD] Fix MTD device probing

Try larger numbers of chips before smaller
numbers of chips across the bus width.

This means we'll avoid misdetecting a 2 x16 array as 1 x32 if the
high 16-bits happen to read as zeros in the QRY area.

Signed-off-by: Russell King <linux@arm.linux.org.uk>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>