Add newline to fix documentation build

llvm/docs/AMDGPUUsage.rst

- .name: hello_world
            .actual_access: write_only
    //...
    .end_amdgpu_metadata
 
 This kernel is equivalent to the following HIP program:
 
 .. code::
    :number-lines:
+
    __global__ void hello_world(float *p) {
        *p = 3.14159f;
    }
 
 If an assembly source file contains multiple kernels and/or functions, the
 :ref:`amdgpu-amdhsa-assembler-symbol-next_free_vgpr` and
 :ref:`amdgpu-amdhsa-assembler-symbol-next_free_sgpr` symbols may be reset using
 the ``.set <symbol>, <expression>`` directive. For example, in the case of two