arm64: zynqmp: Remove information about dma clock on zcu106

Clock setting is not static anymore that's why it depends on firmware setup
that's why remove this comment.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Link: https://lore.kernel.org/r/17973ffda4e163a4b89d4732fe6fc7e089962ae7.1623684253.git.michal.simek@xilinx.com