[ALSA] opl4 depends on opl3

OPL3
Compiling OPL4 doesn't include the snd-opl3-lib. This change in the
Makefile enables now the compiling of snd-opl3-lib.o for OPL4 soundcards.
Signed-off-by: Martin Langer <martin-langer@gmx.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/drivers/opl3/Makefile

@@ -18,4 +18,5 @@ endif
 sequencer = $(if $(subst y,,$(CONFIG_SND_SEQUENCER)),$(if $(1),m),$(if $(CONFIG_SND_SEQUENCER),$(1)))
 
 obj-$(CONFIG_SND_OPL3_LIB) += snd-opl3-lib.o
+obj-$(CONFIG_SND_OPL4_LIB) += snd-opl3-lib.o
 obj-$(call sequencer,$(CONFIG_SND_OPL3_LIB)) += snd-opl3-synth.o