seafile-server: fix patch file

Signed-off-by: Gergely Kiss <mail.gery@gmail.com>

net/seafile-server/patches/050-libseafile-makefile-fixes.patch

@@ -30,7 +30,7 @@ diff -rupN seafile-server-5.1.1.orig/lib/Makefile.am seafile-server-5.1.1/lib/Ma
  	@rm -f vala.tmp
  	@touch vala.tmp
 -	valac -C --pkg posix $^
-+	"$(STAGING_DIR_HOST)/host/bin/valac" -C --pkg posix $^
++	"$(STAGING_DIR)/host/bin/valac" -C --pkg posix $^
  	@mv -f vala.tmp $@
  
  ${seafile_object_gen}: vala.stamp