Support higher tuning frequencies

Static analysis (coverity) detected that some of the
math computing frequencies was performed in 32 bit
arithmetic, even though the result was 64 bits.  This
could result in an integer overflow.  Use the Qt
long long type to move to 64 bit calculations.

Fixes coverity 700586
Fixes #11594

Signed-off-by: Daniel Kristjansson <danielk@cuymedia.net>