drm/amdgpu/gfx12: fix wptr reset in KGQ init

drm/amdgpu/gfx12: fix wptr reset in KGQ init

commit 9077d32a4b570fa20500aa26e149981c366c965d upstream.

wptr is a 64 bit value and we need to update the
full value, not just 32 bits. Align with what we
already do for KCQs.

Reviewed-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Jesse Zhang <jesse.zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit a2918f958d3f677ea93c0ac257cb6ba69b7abb7c)
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>