rtc: mxc: Use devm_clk_get_enabled() helper

rtc: mxc: Use devm_clk_get_enabled() helper

The devm_clk_get_enabled() helper:
   - calls devm_clk_get()
   - calls clk_prepare_enable() and registers what is needed in order to
     call clk_disable_unprepare() when needed, as a managed resource.

This simplifies the code, the error handling paths and avoid the need of
a dedicated function used with devm_add_action_or_reset().

Based on my test with allyesconfig, this reduces the .o size from:
   text	   data	    bss	    dec	    hex	filename
   6705	   1968	      0	   8673	   21e1	drivers/rtc/rtc-mxc.o
down to:
   6212	   1968	      0	   8180	   1ff4	drivers/rtc/rtc-mxc.o

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/1b5ad1877304b01ddbba73ca615274a52f781aa2.1660582728.git.christophe.jaillet@wanadoo.fr