objdump: fix extended (256) disassembler colors

After commit:

  commit a88c79b770
  Date:   Tue Aug 9 14:57:48 2022 +0100

      Default to enabling colored disassembly if output is to a terminal.

The 256 extended-color support for --disassembler-color was broken.
This is fixed in this commit.

	PR 29457
	* objdump (objdump_styled_sprintf): Check disassembler_color
	against an enum value, don't treat it as a bool.

binutils/objdump.c

@@ -2247,7 +2247,7 @@ objdump_styled_sprintf (SFILE *f, enum disassembler_style style,
 	{
 	  size_t space = f->alloc - f->pos;
 
-	  if (disassembler_color)
+	  if (disassembler_color == on)
 	    n = snprintf (f->buffer + f->pos, space, "\033[%dm", color);
 	  else
 	    n = snprintf (f->buffer + f->pos, space, "\033[38;5;%dm", color);