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

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

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

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

v2: fixed dri_search_path by default, rebased to master

v3: new commit-message (Emil Velikov), cc mesa-stable

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=109698
CC: Rafael Antognolli <rafael.antognolli@intel.com>
CC: Dylan Baker <dylan@pnwbakers.com>
Cc: 18.3 19.0 <mesa-stable@lists.freedesktop.org>
Fixes: 306914db92e1 (meson: Add dridriverdir variable to dri.pc.)
Signed-off-by: Sergii Romantsov <sergii.romantsov@globallogic.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
diff --git a/meson.build b/meson.build
index 44bc2f7..8cac9f6 100644
--- a/meson.build
+++ b/meson.build
@@ -61,11 +61,11 @@
 
 dri_drivers_path = get_option('dri-drivers-path')
 if dri_drivers_path == ''
-  dri_drivers_path = join_paths(get_option('libdir'), 'dri')
+  dri_drivers_path = join_paths(get_option('prefix'), get_option('libdir'), 'dri')
 endif
 dri_search_path = get_option('dri-search-path')
 if dri_search_path == ''
-  dri_search_path = join_paths(get_option('prefix'), dri_drivers_path)
+  dri_search_path = dri_drivers_path
 endif
 
 with_gles1 = get_option('gles1')