arm64: dts: imx8mq-librem5: Bump usdhc2 frequency to 100MHz

RS9116 card already limits itself to 50MHz by being a high-speed card,
while AP6275S can work at 100MHz just fine (technically it should work
at 200MHz as well since it's a SDR104 card, but it doesn't appear to be
the case in practice and further research will be needed to find out why).

Signed-off-by: Sebastian Krzyszkowiak <sebastian.krzyszkowiak@puri.sm>
Signed-off-by: Martin Kepplinger <martin.kepplinger@puri.sm>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>