Fix printing & reading of 16-bit CFI device identifiers

Fix reading and printing of CFI flashes 16-bit devices identifiers

Nowadays CFI flashes have a 16-bit device identifier.  U-boot still
print them and read them as if they were only 8-bit wide.  Fix that.
Before:
  Intel Extended command set, Manufacturer ID: 0x89, Device ID: 0x1B
After:
  Intel Extended command set, Manufacturer ID: 0x89, Device ID: 0x881B

Signed-off-by: Philippe De Muyter <phdm@macqel.be>
Signed-off-by: Stefan Roese <sr@denx.de>