qga: fix 'driver' leak in guest-get-fsinfo

'driver' is leaked when the loop is not broken.

Leak introduced by commit 743c71d03c,
spotted by ASAN.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

qga/commands-posix.c

@@ -890,6 +890,7 @@ static void build_guest_fsinfo_for_real_device(char const *syspath,
             break;
         }
 
+        g_free(driver);
         if (sscanf(p, "/%x:%x:%x.%x%n",
                           pci, pci + 1, pci + 2, pci + 3, &pcilen) == 4) {
             p += pcilen;