Informative error if memory to burn is less than threshold

[ashuthak210]

[Problem]
If the %age memory to burn is below a threshold then program aborts without any user friendly message.

[Solution]
Added a user friendly message that can save debugging for the user

[Testing]
Testing with following run

ashuthak@ashuthak-ubuntu:~/gpu_burn/gpu-burn$ ./gpu_burn -m 1% 60
Using compare file: compare.ptx
Burning for 60 seconds.
GPU 0: NVIDIA GeForce RTX 4060 Laptop GPU (UUID: GPU-062ffaaa-3ab3-31f9-1938-451fee6a15fb)
Initialized device 0 with 7721 MB of memory (7594 MB available, using 75 MB of it), using FLOATS
Results are 268435456 bytes each, thus performing 68719476734 iterations
Provide bytes (75 MB) are not sufficient. aborting.
terminate called after throwing an instance of 'std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >'
1.7%  proc'd: -1 (0 Gflop/s)   errors: 0  (DIED!)  temps: 49 C