r the
polling devready function.  So switch it over to use the BUSY bit in the
STAT register that always reflects the current state of the hardware.

This fixes driver hangs seen when the NAND flash is under heavy system
load (like I/O benchmarks).

Signed-off-by: Barry Song <barry.song@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>