iio: adc: rcar-gyroadc: Drop if clock from Renesas GyroADC bindings

The "if" interface clock speed is actually derived from the "fck"
block clock, as in the hardware they are the same clock. Drop the
incorrect second "if" clock and retain only the "fck" clock.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Rob Herring <robh@kernel.org>
Cc: linux-renesas-soc@vger.kernel.org
To: devicetree@vger.kernel.org
Signed-off-by: Jonathan Cameron <jic23@kernel.org>