d3d: meson: do not prefix user provided d3d-drivers-path

The user can select the location where there d3d drivers
are installed by the d3d-drivers-path meson option.

By default path will be $prefix/$libdir/d3d.

Currently we add $prefix to the user provided path.
Resulting in an incorrect or even missing path.

Based on logic of
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=109698
CC: Kenneth Graunke <kenneth@whitecape.org>
CC: Emil Velikov <emil.l.velikov@gmail.com>
Signed-off-by: Sergii Romantsov <sergii.romantsov@globallogic.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>

meson.build

@@ -610,7 +610,7 @@ with_gallium_xa = _xa != 'false'
 
 d3d_drivers_path = get_option('d3d-drivers-path')
 if d3d_drivers_path == ''
-  d3d_drivers_path = join_paths(get_option('libdir'), 'd3d')
+  d3d_drivers_path = join_paths(get_option('prefix'), get_option('libdir'), 'd3d')
 endif
 
 with_gallium_st_nine =  get_option('gallium-nine')

src/gallium/targets/d3dadapter9/meson.build

@@ -68,5 +68,5 @@ pkg.generate(
   description : 'Native D3D driver modules',
   version : '.'.join(nine_version),
   requires_private : 'libdrm >= ' + dep_libdrm.version(),
-  variables : ['moduledir=${prefix}/@0@'.format(d3d_drivers_path)],
+  variables : ['moduledir=@0@'.format(d3d_drivers_path)],
 )