spi: atmel-quadspi: return appropriate error code

Return -ENOTSUPP when atmel_qspi_find_mode() fails. Propagate
the error in atmel_qspi_exec_op().
Signed-off-by: NTudor Ambarus <tudor.ambarus@microchip.com>
Reviewed-by: NBoris Brezillon <bbrezillon@kernel.org>
Signed-off-by: NMark Brown <broonie@kernel.org>

drivers/spi/atmel-quadspi.c

@@ -198,7 +198,7 @@ static int atmel_qspi_find_mode(const struct spi_mem_op *op)
 		if (atmel_qspi_is_compatible(op, &sama5d2_qspi_modes[i]))
 			return i;
 
-	return -1;
+	return -ENOTSUPP;
 }
 
 static bool atmel_qspi_supports_op(struct spi_mem *mem,
@@ -238,7 +238,7 @@ static int atmel_qspi_exec_op(struct spi_mem *mem, const struct spi_mem_op *op)
 
 	mode = atmel_qspi_find_mode(op);
 	if (mode < 0)
-		return -ENOTSUPP;
+		return mode;
 
 	ifr |= sama5d2_qspi_modes[mode].config;