vl.c: Print the actual program name in help output

In help() we do what boils down to:

  printf("%s", "qemu");

This seems to be an artifact of be995c27640a82c7056b6f53d02ec823570114e5
("removed unused code"), which removed some ifdef'ery that used to print
a different name depending on CONFIG_SOFTMMU.

Instead print the actual program name, originally from argv[0].

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

vl.c

@@ -1513,7 +1513,7 @@ static void help(int exitcode)
            "ctrl-alt        toggle mouse and keyboard grab\n"
            "\n"
            "When using -nographic, press 'ctrl-a h' to get some help.\n",
-           "qemu",
+           error_get_progname(),
            options_help);
     exit(exitcode);
 }