hwmon: (nzxt-smart2) Use devm_mutex_init()

hwmon: (nzxt-smart2) Use devm_mutex_init()

Use devm_mutex_init() instead of hand-writing it.

This saves some LoC, improves readability and saves some space in the
generated .o file.

Before:
======
   text	   data	    bss	    dec	    hex	filename
  25878	  11329	    128	  37335	   91d7	drivers/hwmon/nzxt-smart2.o

After:
=====
   text	   data	    bss	    dec	    hex	filename
  25551	  11257	    128	  36936	   9048	drivers/hwmon/nzxt-smart2.o

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/f51fac0871ec7dbe4e28447ee4f774d028a53426.1757240403.git.christophe.jaillet@wanadoo.fr
Signed-off-by: Guenter Roeck <linux@roeck-us.net>