ALSA: Fix forgotten dependency fix for tristate OSS sequencer kconfig

In the commit 3d774d5e ("ALSA: seq: Allow the tristate build of
OSS emulation") we changed CONFIG_SND_SEQUENCER_OSS to tristate, but a
couple of places were forgotten, namely, opl3 and emux Makefile.
These contain the line like
  snd-opl3-synth-$(CONFIG_SND_SEQUENCER_OSS) += opl3_oss.o
and this doesn't work any longer as expected because snd-opl3-synth
can be built-in while CONFIG_SND_SEQUENCER_OSS=m.

This patch fixes these places to build properly for the new kconfig
dependency.  In the end, we had to use ifneq() to satisfy the
requirement.  It's a bit ugly, but lesser evil.

Fixes: 3d774d5e ("ALSA: seq: Allow the tristate build of OSS emulation")
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/drivers/opl3/Makefile

@@ -5,7 +5,9 @@
 
 snd-opl3-lib-objs := opl3_lib.o opl3_synth.o
 snd-opl3-synth-y := opl3_seq.o opl3_midi.o opl3_drums.o
-snd-opl3-synth-$(CONFIG_SND_SEQUENCER_OSS) += opl3_oss.o
+ifneq ($(CONFIG_SND_SEQUENCER_OSS),)
+snd-opl3-synth-y += opl3_oss.o
+endif
 
 obj-$(CONFIG_SND_OPL3_LIB) += snd-opl3-lib.o
 obj-$(CONFIG_SND_OPL4_LIB) += snd-opl3-lib.o

sound/synth/emux/Makefile

@@ -6,6 +6,8 @@
 snd-emux-synth-objs := emux.o emux_synth.o emux_seq.o emux_nrpn.o \
 		       emux_effect.o emux_hwdep.o soundfont.o
 snd-emux-synth-$(CONFIG_SND_PROC_FS) += emux_proc.o
-snd-emux-synth-$(CONFIG_SND_SEQUENCER_OSS) += emux_oss.o
+ifneq ($(CONFIG_SND_SEQUENCER_OSS),)
+snd-emux-synth-y += emux_oss.o
+endif
 
 obj-$(CONFIG_SND_SYNTH_EMUX) += snd-emux-synth.o