drm/amdgpu: Change amdgpu_ras_block_late_init_default function scope

Turn previously global function into a static function to avoid the
following Clang warning:

drivers/gpu/drm/amd/amdgpu/amdgpu_ras.c:2459:5: warning: no previous prototype
for function 'amdgpu_ras_block_late_init_default' [-Wmissing-prototypes]
int amdgpu_ras_block_late_init_default(struct amdgpu_device *adev,
    ^
drivers/gpu/drm/amd/amdgpu/amdgpu_ras.c:2459:1: note: declare 'static' if the
function is not intended to be used outside of this translation unit
int amdgpu_ras_block_late_init_default(struct amdgpu_device *adev,
^
static

Signed-off-by: Maíra Canal <maira.canal@usp.br>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>