Current ath79 clock.c code does not read reference clock and
pll setup from devicetree. The ar724x_clocks_init() function
recreates the clocks from scratch so devicetree clock
information is dropped. After adding the code which picked up
reference clock from devicetree I have found
that kernel does not boot anymore. The SPI and UART drivers
can't get clk; here are the bootlog error messages:

    of_serial: probe of 18020000.uart failed with error -22
    ath79-spi: probe of 1f000000.spi failed with error -22

The problem is that clock code assumes that reference clock
name is "ref" but current dts-file uses another name: "oscillator".

This patch fixes the problem by changing external oscillator
dt node name to "ref".

Please note that there is an alternative solution for the problem:

    > --- a/arch/mips/boot/dts/qca/ar9132_tl_wr1043nd_v1.dts
    > +++ b/arch/mips/boot/dts/qca/ar9132_tl_wr1043nd_v1.dts
    > @@ -16,6 +16,7 @@
    >
    >         extosc: oscillator {
    >                 compatible = "fixed-clock";
    > +               clock-output-names = "ref";
    >                 #clock-cells = <0>;
    >                 clock-frequency = <40000000>;
    >         };
Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>
Cc: Alban Bedel <albeu@free.fr>
Cc: Michael Turquette <mturquette@baylibre.com>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: linux-clk@vger.kernel.org
Cc: linux-mips@linux-mips.org
Cc: devicetree@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/12874/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>