MIPS: dts: mscc: Updated changed name for miim pinctrl function

MIPS: dts: mscc: Updated changed name for miim pinctrl function

This is an add-on patch to the main SoC Sparx5 series
(Message-ID: <20200513125532.24585-1-lars.povlsen@microchip.com>).

This changes the miim pinctrl function name from "miim1" to "miim" due
to refactoring in the driver, obsoleting the instance number.

The change in the driver was to better fit new platforms, as the
instance number is redundant information. Specifically, support for
the Microchip Sparx5 SoC is being submitted, where this change became
necessary.

Reviewed-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Lars Povlsen <lars.povlsen@microchip.com>
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>