ARM: at91/dt: sama5d4 master clock can run at 200MHz now

After the change of frequency a SAMA5D4 can reach, we have to modify the
maximum clock specification for the master clock, up to 200MHz now.

It avoids the wrong message saying that "master clk is overclocked" for this
configuration.

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>