leds: is31fl319x: Use devm_mutex_init()

leds: is31fl319x: 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
  20011	   6752	    128	  26891	   690b	drivers/leds/leds-is31fl319x.o

After:
=====
   text	   data	    bss	    dec	    hex	filename
  19715	   6680	    128	  26523	   679b	drivers/leds/leds-is31fl319x.o

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/267aba6eab12be67c297fcd52fcf45a0856338bb.1757240150.git.christophe.jaillet@wanadoo.fr
Signed-off-by: Lee Jones <lee@kernel.org>