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

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>