drm/amdgpu: fix PA_SC_FIFO_SIZE for Navi10 (v2)

Proper size is 0.

v2: squash in whitespace fixes (Ernst Sjöstrand)

Signed-off-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Xiaojie Yuan <xiaojie.yuan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>