ARM: dts: imx6q-tbs2910: fix pcie reset polarity

According to Documentation/devicetree/bindings/pci/fsl,imx6q-pcie.txt the
polarity of "reset-gpio" is assumed to be active-low unless a separate
property "reset-gpio-active-high" is available. So replace the inconsistent
polarity description to make the correct active-low reset behavior more
obvious.

Signed-off-by: Soeren Moch <smoch@web.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>