ARM: dts: keystone: drop msmcsram clock node

At late init all unused clocks are disabled. So clocks that were not
get before will be gated. In Keysone 2 SoC we have at least one
necessary clock that is not used by any driver - "msmcsram". This
clock is necessary, because it supplies the Multicore Shared Memory
Controller (MSMC). MSMC is the coherency interconnect and all the
coherent masters are connected to it including devices which are not
under Linux OS control. MSMC clock should not be touched even in low
power states.

So drop the clock node, otherwise 'clk_ignore_unused' parameter will
disable the clock leading to system stall.

Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@ti.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>