sigProcLib: Specify standard namespace for isnan()

In commit a3dce85f
"sigProcLib: Use explicit NaN check in sinc table generation"

Use of std::isnan(double) was added without namespace specifier,
which may cause build issues depending on whether the C version
isnan() call is available. Add standard namespace to force C++
call usage and potential build issues.

Change-Id: I49328c43fdd690a4e6a2b2e949411aaf5674ead1
1 file changed