i2c/mips: Fix error return codes from Sibyte i2c bus driver

Sibyte i2c bus driver returns non-descriptive error values.
Update to return error values as defined in Documentation/i2c/fault-codes.

Signed-off-by: Guenter Roeck <[e-mail]>
Signed-off-by: Jean Delvare <[e-mail]>

drivers/i2c/busses/i2c-sibyte.c

···
 		}
 		break;
 	default:
-		return -1;      /* XXXKW better error code? */
+		return -EOPNOTSUPP;
 	}
 
 	while (csr_in32(SMB_CSR(adap, R_SMB_STATUS)) & M_SMB_BUSY)
···
 	if (error & M_SMB_ERROR) {
 		/* Clear error bit by writing a 1 */
 		csr_out32(M_SMB_ERROR, SMB_CSR(adap, R_SMB_STATUS));
-		return -1;      /* XXXKW better error code? */
+		return (error & M_SMB_ERROR_TYPE) ? -EIO : -ENXIO;
 	}
 
 	if (data_bytes == 1)