In function onenand_verify_oob, local variable oobbuf shall be unsigned char.

In the case of a value is >= 0x80, it's unequal in comparing the value in an unsigned char and signed char.
Signed-off-by: NSheng Yongjie (Sam) <samsheng@trident.com.cn>
Signed-off-by: NKyungmin Park <kyungmin.park@samsung.com>