binman: Drop __bss_size variable in bss_data.c

This is not needed since the linker script sets it up. Drop the variable
to avoid confusion.

Fix the prototype for main() while we are here.

Signed-off-by: Simon Glass <sjg@chromium.org>

tools/binman/test/bss_data.c

@@ -7,9 +7,8 @@
  */
 
 int bss_data[10];
-int __bss_size = sizeof(bss_data);
 
-int main()
+int main(void)
 {
 	bss_data[2] = 2;