leds: leds-lp3944: Provide missing function names in documentation headers

Fixes the following W=1 kernel build warning(s):

 drivers/leds/leds-lp3944.c:95: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 drivers/leds/leds-lp3944.c:126: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 drivers/leds/leds-lp3944.c:158: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst

Cc: Pavel Machek <pavel@ucw.cz>
Cc: Antonio Ospite <ospite@studenti.unina.it>
Cc: linux-leds@vger.kernel.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Pavel Machek <pavel@ucw.cz>