[MTD] NAND: Fix broken bad block scan for 16 bit devices

The previous change to read a single byte from oob breaks the
bad block scan on 16 bit devices, when the byte is on an odd
address. Read the complete oob for now.
Remove the unused arguments from check_short_pattern()
Move the wait for ready function so it is only executed when
consecutive reads happen.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>