ARM: dts: imx6qdl-kontron-samx6i: fix PCIe reset polarity

[ Upstream commit df35c6e9027cf9affe699e632a48082ab1bbba4c ]

The PCIe reset line is active low. Fix it.

Fixes: 2a51f9da ("ARM: dts: imx6qdl-kontron-samx6i: Add iMX6-based Kontron SMARC-sAMX6i module")
Signed-off-by: Michael Walle <mwalle@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>