mtd: rawnand: qcom: Handle unsupported opcode in qcom_op_cmd_mapping()

Handle the scenario where the caller has passed an unsupported opcode to
qcom_op_cmd_mapping(). In that case, log the error and return the
-EOPNOTSUPP errono. Also, let's propagate this error code all the way up.

This also fixes the following smatch warning:

drivers/mtd/nand/raw/qcom_nandc.c:2941 qcom_op_cmd_mapping() error: uninitialized symbol 'ret'.

Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/r/202308032022.SnXkKyFs-lkp@intel.com/
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20230805174146.57006-4-manivannan.sadhasivam@linaro.org