mtd: rawnand: qcom: Fix read len for onfi param page

The minimum size to fetch the data from device to QPIC buffer
is 512-bytes. If size is less than 512-bytes the data will not be
protected by ECC as per QPIC standard. So while reading onfi parameter
page from NAND device set nandc->buf_count = 512.

Cc: stable@vger.kernel.org
Fixes: 89550beb ("mtd: rawnand: qcom: Implement exec_op()")
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Tested-by: Lakshmi Sowjanya D <quic_laksd@quicinc.com>
Signed-off-by: Md Sadre Alam <quic_mdalam@quicinc.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>