mtd: nand: remove redundant ID read

Instead of reading 2 bytes then later 8 bytes, we can simply read all 8
bytes from the start.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>