uhd: branch-less round for time spec convert to ticks

This fixes valgrind warnings with branching on unit'd values,
and possible exceptions thrown on bad unit'd values.

As it turns out, sometimes tick_rate was passed unit'd,
however, the value calculated was not of consequence.

Also, iround was overkill because we dont need to handle
negative tick rates or frac seconds, or bounds checking.

host/lib/types/time_spec.cpp

@@ -16,7 +16,6 @@
 //
 
 #include <uhd/types/time_spec.hpp>
-#include <boost/math/special_functions/round.hpp>
 
 using namespace uhd;
 
@@ -109,7 +108,7 @@ time_spec_t::time_spec_t(time_t full_secs, long tick_count, double tick_rate){
  * Time spec accessors
  **********************************************************************/
 long time_spec_t::get_tick_count(double tick_rate) const{
-    return boost::math::iround(this->get_frac_secs()*tick_rate);
+    return long(this->get_frac_secs()*tick_rate + 0.5);
 }
 
 double time_spec_t::get_real_secs(void) const{