depends: fix typo in source downloading. Regression from c897b1e732.

Some sources are renamed after download, since the filenames don't play nice
with (for example) gitian. This fixes the rename.

Needed for OSX build as it renames a file.

depends/funcs.mk

@@ -22,8 +22,8 @@ endef
 define fetch_file
 (test -f $(SOURCES_PATH)/$(4) || \
   ( mkdir -p $$($(1)_extract_dir) && \
-  ( $(build_DOWNLOAD) "$$($(1)_extract_dir)/$(3).temp" "$(2)/$(3)" || \
-    $(build_DOWNLOAD) "$$($(1)_extract_dir)/$(3).temp" "$(FALLBACK_DOWNLOAD_PATH)/$(3)" ) && \
+  ( $(build_DOWNLOAD) "$$($(1)_extract_dir)/$(4).temp" "$(2)/$(3)" || \
+    $(build_DOWNLOAD) "$$($(1)_extract_dir)/$(4).temp" "$(FALLBACK_DOWNLOAD_PATH)/$(3)" ) && \
     echo "$(5)  $$($(1)_extract_dir)/$(4).temp" > $$($(1)_extract_dir)/.$(4).hash && \
     $(build_SHA256SUM) -c $$($(1)_extract_dir)/.$(4).hash && \
     mv $$($(1)_extract_dir)/$(4).temp $(SOURCES_PATH)/$(4) ))