mplayer: make sure alsa-lib is installed before mplayer

This patch adds alsa-lib to a dependency for mplayer if it is selected in
kconfig.

Signed-off-by: Hans-Christian Egtvedt <hans-christian.egtvedt@atmel.com>

package/multimedia/mplayer/mplayer.mk

@@ -19,6 +19,10 @@ endif
 
 MPLAYER_DEP_LIBS:=libmad
 
+ifeq ($(strip $(BR2_PACKAGE_ALSA_LIB)),y)
+MPLAYER_DEP_LIBS+=alsa-lib
+endif
+
 $(DL_DIR)/$(MPLAYER_SOURCE):
 	$(WGET) -P $(DL_DIR) $(MPLAYER_SITE)/$(MPLAYER_SOURCE)