[MTD] Fixup probing logic for single 16bit devices

The change to the generic probe to look for the
smallest width of chip first is causing some problems
on boards with a single 16bit device.

The problem seems to be the jedec_match() is truncating
the device-id read from the table to match against the
one read from the hardware, causing a match against the
partial id of some chips with 16bit IDs (such as the
SST39LF160)

This fixes things for my own board, but something may
need to be done if the same problem is exhibited for
chips with an 8bit ID

Signed-off-by: Ben Dooks <ben@simtec.co.uk>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>