dt-bindings: spi: atmel-quadspi: make "pclk" mandatory

Naming clocks is a good practice. Make "pclk" madatory even if
we support unnamed clock in the driver, to be backward compatible
with old DTs.
Suggested-by: NBoris Brezillon <bbrezillon@kernel.org>
Signed-off-by: NTudor Ambarus <tudor.ambarus@microchip.com>
Reviewed-by: NBoris Brezillon <bbrezillon@kernel.org>
Signed-off-by: NMark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/spi/atmel-quadspi.txt

@@ -9,6 +9,7 @@ Required properties:
                   - qspi_mmap: memory mapped address space
 - interrupts:     Should contain the interrupt for the device.
 - clocks:         The phandle of the clock needed by the QSPI controller.
+- clock-names:    Should contain "pclk" for the peripheral clock.
 - #address-cells: Should be <1>.
 - #size-cells:    Should be <0>.
 
@@ -20,6 +21,7 @@ spi@f0020000 {
 	reg-names = "qspi_base", "qspi_mmap";
 	interrupts = <52 IRQ_TYPE_LEVEL_HIGH 7>;
 	clocks = <&pmc PMC_TYPE_PERIPHERAL 52>;
+	clock-names = "pclk";
 	#address-cells = <1>;
 	#size-cells = <0>;
 	pinctrl-names = "default";