rtc: st-lpc: Simplify clk handling in st_rtc_probe()

Use devm_clk_get_enabled() instead of hand writing it. This simplifies
error handling and removes some lines of code.

Also use dev_err_probe() which filters -EPROBE_DEFER.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/992dd8c31be0bb5b8a9d8b5e8e94807ab0848a66.1686251455.git.christophe.jaillet@wanadoo.fr


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