mplayer: set charset explisit to US-ASCII to ease intl compile

This patch set the charset selected by mplayer to US-ASCII because mplayer
configure script have problems detecting working cross compiled iconv tools

package/multimedia/mplayer/mplayer.mk

@@ -41,6 +41,7 @@ $(MPLAYER_DIR)/.configured: $(MPLAYER_DIR)/.unpacked
 		--as=$(TARGET_CROSS)as \
 		--with-extraincdir=$(STAGING_DIR)/usr/include \
 		--with-extralibdir=$(STAGING_DIR)/lib \
+		--charset=US-ASCII \
 		--enable-mad \
 		--enable-fbdev \
 		$(MPLAYER_ENDIAN) \