bitbake: fetch: use BPN instead

When checking for the non-existing file, BPN is actually the acutal recipe
name. And we should use BPN for the error message and it also fix the below
test when multilib is enabled.
 $ oe-selftest -r bbtests.BitbakeTests.test_invalid_recipe_src_uri

(Bitbake rev: d613e48c07d4b12219270c1359cbf2f390b848dd)

Signed-off-by: Mingli Yu <mingli.yu@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/fetch2/__init__.py

@@ -1236,7 +1236,7 @@ def get_checksum_file_list(d):
             if not found:
                 bb.fatal(("Unable to get checksum for %s SRC_URI entry %s: file could not be found"
                             "\nThe following paths were searched:"
-                            "\n%s") % (d.getVar('PN'), os.path.basename(f), '\n'.join(paths)))
+                            "\n%s") % (d.getVar('BPN'), os.path.basename(f), '\n'.join(paths)))
 
     return " ".join(filelist)