src: meson: Simplify v4l2 enablement

Simplify the src level meson file by moving the declaration of the v4l2
subdir to match the other invocations, making use of 'subdir_done()' to
break out if the adaptation layer is not enabled.

Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

src/meson.build

@@ -21,8 +21,5 @@ subdir('ipa')
 subdir('cam')
 subdir('qcam')
 
-if get_option('v4l2')
-    subdir('v4l2')
-endif
-
 subdir('gstreamer')
+subdir('v4l2')

src/v4l2/meson.build

@@ -1,5 +1,9 @@
 # SPDX-License-Identifier: CC0-1.0
 
+if not get_option('v4l2')
+    subdir_done()
+endif
+
 v4l2_compat_sources = files([
     'v4l2_camera.cpp',
     'v4l2_camera_file.cpp',