dropbear: look for xauth in /usr/bin

The xauth package installs into /usr/bin, so look for it there.

package/dropbear/dropbear.mk

@@ -20,6 +20,7 @@ $(DROPBEAR_DIR)/.unpacked: $(DL_DIR)/$(DROPBEAR_SOURCE)
 	$(DROPBEAR_CAT) $(DL_DIR)/$(DROPBEAR_SOURCE) | tar -C $(BUILD_DIR) $(TAR_OPTIONS) -
 	toolchain/patch-kernel.sh $(DROPBEAR_DIR) package/dropbear/ dropbear\*.patch
 	$(SED) 's,^/\* #define DROPBEAR_MULTI.*,#define DROPBEAR_MULTI,g' $(DROPBEAR_DIR)/options.h
+	$(SED) 's,^#define XAUTH_COMMAND.*/xauth,#define XAUTH_COMMAND "/usr/bin/xauth,g' $(DROPBEAR_DIR)/options.h
 	$(CONFIG_UPDATE) $(DROPBEAR_DIR)
 	touch $@