Correct the specified regulator-min-microvolt value for the buck DCDC_REG2
regulator, which is part of the Rockchip RK809 PMIC, in the Pine64 Quartz64
Model B board dts.  According to the RK809 datasheet, version 1.01, this
regulator is capable of producing voltages as low as 0.5 V on its output,
instead of going down to 0.9 V only, which is additionally confirmed by the
regulator-min-microvolt values found in the board dts files for the other
supported boards that use the same RK809 PMIC.

This allows the DVFS to clock the GPU on the Quartz64 Model B below 700 MHz,
all the way down to 200 MHz, which saves some power and reduces the amount of
generated heat a bit, improving the thermal headroom and possibly improving
the bursty CPU and GPU performance on this board.

This also eliminates the following warnings in the kernel log:

  core: _opp_supported_by_regulators: OPP minuV: 825000 maxuV: 825000, not supported by regulator
  panfrost fde60000.gpu: _opp_add: OPP not supported by regulators (200000000)
  core: _opp_supported_by_regulators: OPP minuV: 825000 maxuV: 825000, not supported by regulator
  panfrost fde60000.gpu: _opp_add: OPP not supported by regulators (300000000)
  core: _opp_supported_by_regulators: OPP minuV: 825000 maxuV: 825000, not supported by regulator
  panfrost fde60000.gpu: _opp_add: OPP not supported by regulators (400000000)
  core: _opp_supported_by_regulators: OPP minuV: 825000 maxuV: 825000, not supported by regulator
  panfrost fde60000.gpu: _opp_add: OPP not supported by regulators (600000000)

Fixes: dcc8c66b ("arm64: dts: rockchip: add Pine64 Quartz64-B device tree")
Cc: stable@vger.kernel.org
Reported-By: Diederik de Haas <didi.debian@cknow.org>
Signed-off-by: Dragan Simic <dsimic@manjaro.org>
Tested-by: Diederik de Haas <didi.debian@cknow.org>
Link: https://lore.kernel.org/r/e70742ea2df432bf57b3f7de542d81ca22b0da2f.1716225483.git.dsimic@manjaro.orgSigned-off-by: Heiko Stuebner <heiko@sntech.de>