plugins/fmcomms5.c: Fix MCS trigger with not effect
Multi Chip Synchronization is done after a sampling frequency change in the plugin. However the synchronization has no effect while using certain frequency values (30.70, 31.70, 60.71 are just a couple of them).
The solution (workaround) is to schedule the MCS to be called later (couple of ms).

Signed-off-by: Dan Nechita <dan.nechita@analog.com>