qemu-pr-helper: Actually allow users to specify pidfile

Due to wrong specification of arguments to getopt_long() any
attempt to set pidfile resulted in:

1) the default to be leaked
2) the @pidfile variable to be set to NULL (because optarg is
NULL without this patch).

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Message-Id: <6f10cd53d361a395aa0e85a9311ec4e9a8fc11e5.1521868451.git.mprivozn@redhat.com>
Cc: qemu-stable@nongnu.org
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

scsi/qemu-pr-helper.c

@@ -903,12 +903,12 @@ static int drop_privileges(void)
 
 int main(int argc, char **argv)
 {
-    const char *sopt = "hVk:fdT:u:g:vq";
+    const char *sopt = "hVk:f:dT:u:g:vq";
     struct option lopt[] = {
         { "help", no_argument, NULL, 'h' },
         { "version", no_argument, NULL, 'V' },
         { "socket", required_argument, NULL, 'k' },
-        { "pidfile", no_argument, NULL, 'f' },
+        { "pidfile", required_argument, NULL, 'f' },
         { "daemon", no_argument, NULL, 'd' },
         { "trace", required_argument, NULL, 'T' },
         { "user", required_argument, NULL, 'u' },
@@ -952,7 +952,8 @@ int main(int argc, char **argv)
             }
             break;
         case 'f':
-            pidfile = optarg;
+            g_free(pidfile);
+            pidfile = g_strdup(optarg);
             break;
 #ifdef CONFIG_LIBCAP
         case 'u': {