[NVPTX][DebugInfo] avoid emitting extra .loc directives (#84584)

This change removes an extra, unneeded debug directive emitted in the
PTX at the beginning on non-empty functions:
```nvptx
.visible .func  (.param .b32 func_retval0) foo(
        .param .b32 foo_param_0,
        .param .b32 foo_param_1
)
{
        .reg .b32    %r<4>;
        .loc    1 26 0             <---- unneeded (removed by the PR)
$L__func_begin0:
        .loc    1 26 0
```