build/cmake: Fix udev related warning

CMake Warning (dev) at /usr/share/cmake-3.18/Modules/FindPackageHandleStandardArgs.cmake:273 (message):
The package name passed to `find_package_handle_standard_args` (UDEV) does
not match the name of the calling package (udev). This can lead to
problems in calling code that expects `find_package` result variables
(e.g., `_FOUND`) to follow a certain pattern.
Call Stack (most recent call first):
cmake/Findudev.cmake:64 (find_package_handle_standard_args)
CMakeLists.txt:71 (find_package)

cmake/Findudev.cmake

···
 	)
 
 include(FindPackageHandleStandardArgs)
-find_package_handle_standard_args(UDEV
+find_package_handle_standard_args(udev
 	DEFAULT_MSG
 	UDEV_LIBRARY
 	UDEV_INCLUDE_DIR