meson: Add moduledir to d3d.pc

This is required to build wine with the nine patchset

Fixes: 6b4c7047d5
       ("meson: build gallium nine state_tracker")
Reported-by: Mike Lothian <mike@fireburn.co.uk>
Signed-off-by: Dylan Baker <dylan.c.baker@intel.com>
Reviewed-by: Eric Engestrom <eric.engestrom@imgtec.com>

src/gallium/targets/d3dadapter9/meson.build

@@ -72,4 +72,5 @@ pkg.generate(
   description : 'Native D3D driver modules',
   version : '.'.join(nine_version),
   requires_private : 'libdrm >= 2.4.75',
+  variables : ['moduledir=${prefix}/@0@'.format(d3d_drivers_path)],
 )