configure: Update configure so that open_by_handle_at check returns correct value

According to David Gibson for some compiler/libc combinations, open_by_handle_at
test in configure isn't quite right: because the file_handle pointer is never
dereferenced, gcc doesn't complain even if it is undefined. Change the test
as suggested by him.
Signed-off-by: NAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

configure

@@ -2562,7 +2562,7 @@ fi
 open_by_hande_at=no
 cat > $TMPC << EOF
 #include <fcntl.h>
-int main(void) { struct file_handle *fh; open_by_handle_at(0, fh, 0); }
+int main(void) { struct file_handle fh; open_by_handle_at(0, &fh, 0); }
 EOF
 if compile_prog "" "" ; then
     open_by_handle_at=yes