When parameters were removed from dd_function_table::Viewport (commit
065bd6ff

), radeon_viewport (in both radeon and r200) started generating
a warning.

radeon_common.c: In function 'r200_radeon_viewport':
radeon_common.c:415:15: warning: assignment from incompatible pointer type [enabled by default]
radeon_common.c:419:23: warning: assignment from incompatible pointer type [enabled by default]

I didn't notice this initially, and it's harmless because the function is
never called through the incorrectly typed pointer.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Cc: Marek Olšák <marek.olsak@amd.com>