use to_blas_int to check overflow and convert int64_t

[mgates3]

Updates rot, rotm. Other routines already used to_blas_int. Check files:

blaspp/src> git re -l '\bblas_int\b' | xargs grep -L to_blas_int

blaspp/src> git re -l '\bdevice_blas_int\b' | xargs grep -L to_device_blas_int
cublas_wrappers.cc
device_utils.cc
onemkl_wrappers.cc
rocblas_wrappers.cc

blaspp/src> git re numeric_limits
blas_internal.hh:        blas_error_if_msg( x > std::numeric_limits<blas_int>::max(), "%s", x_str );
device_internal.hh:        blas_error_if_msg( std::abs( x ) > std::numeric_limits<device_blas_int>::max(),

[mgates3]

Reviewed.