nand/denali: change read_status function method

In mtd->write, Denali controller will use MODE_11 mode to read
NAND flash status, then return back to MODE_1O mode to do page
write.
Here comes a bug for this kind of using, sometimes controller will
not write data to NAND and just return a good interrupt to tell
driver writing work is done. The data in this page is all 0xff and
this page can not be written again. The reason is unknow.

So read Denali controller register WRITE_PROTECT to get NAND status
instead.

Signed-off-by: Chuanxiao Dong <chuanxiao.dong@intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>