linux-v4l2: Add include directory to cmake

Add the include directories found by cmake to the v4l2 plugin.
This allows for the plugin to compile when the vl42 headers were
found in a directory that is not normally in the search path of the
compiler (e.g. /usr/local/include)

plugins/linux-v4l2/CMakeLists.txt

@@ -24,6 +24,11 @@ else()
 	add_definitions(-DHAVE_UDEV)
 endif()
 
+include_directories(
+	SYSTEM "${CMAKE_SOURCE_DIR}/libobs"
+	${LIBV4L2_INCLUDE_DIRS}
+)
+
 set(linux-v4l2_SOURCES
 	linux-v4l2.c
 	v4l2-input.c