arm64: dts: rockchip: fix reset-names for rk356x i2s2 controller

The dtbscheck reports a warning for a wrong reset-names property for
the i2s2 controller on rk356x socs.

The other controllers on the soc provide tx and rx directions and hence
two resets and separate clocks for each direction, while i2s2 only
provides one reset. This was so far named just "m" which isn't part of
the binding.

The clock-names the controller uses all end in "tx", so use the matching
"tx-m" reset-name for the i2s controller.

Fixes: 755f3701 ("arm64: dts: rockchip: RK356x: Add I2S2 device node")
Acked-by: Uwe Kleine-König <ukleinek@debian.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://lore.kernel.org/r/20240227173526.710056-2-heiko@sntech.de