[][openwrt][common][Fix build error in openssl-fips-ext]

[Description]
Remove Build/Prepare in Makefile.
Make it use default Build/Prepare.

[Release-log]

Change-Id: I5cfa60558c0f9e06779047776f17b4e74b45a5b5
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/8267477
diff --git a/feed/openssl-fips-ext/src/Makefile b/feed/openssl-fips-ext/src/Makefile
index 4d8282e..28e8bab 100644
--- a/feed/openssl-fips-ext/src/Makefile
+++ b/feed/openssl-fips-ext/src/Makefile
@@ -18,4 +18,4 @@
 	$(CC) $(CFLAGS) -c -o common.o $< $(LDFLAGS)
 
 clean:
-	$(RM) openssl-fips-ext
+	$(RM) openssl-fips-ext *.o