HID: lg-g15: make a const array static, makes object smaller

Don't populate the const array led_names on the stack but instead make
it static. Makes the object code smaller by 79 bytes:

Before:
   text	   data	    bss	    dec	    hex	filename
  19686	   7952	    256	  27894	   6cf6	drivers/hid/hid-lg-g15.o

After:
   text	   data	    bss	    dec	    hex	filename
  19543	   8016	    256	  27815	   6ca7	drivers/hid/hid-lg-g15.o

(gcc version 10.2.0)

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>