rtc: Rename lib_test to test_rtc_lib

When compiling the RTC library functions test as a module, the module
has the non-descriptive name "lib_test.ko".  Fix this by renaming it to
"test_rtc_lib.ko".

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Link: https://lore.kernel.org/r/47019d7f8ced12107b54a372fdf34b1b8f7b6183.1751355848.git.geert@linux-m68k.org


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>