mtd: rawnand: qcom: modify write_oob to remove read codeword part

QCOM NAND controller layout protects available OOB data bytes with
ECC also so when ecc->write_oob() is being called then it
can't update just OOB bytes. Currently, it first reads the last
codeword which includes old OOB bytes. Then it updates the old OOB
bytes with new ones and then again writes the codeword back.
The reading codeword is unnecessary since user is responsible to
have these bytes cleared to 0xFF.

This patch removes the read part and updates the OOB bytes with
data area padded with OxFF.

Signed-off-by: Abhishek Sahu <absahu@codeaurora.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>