speakup_audptr: cleanup synth_version

The buffer was bigger than necessary, and the while loop not very
canonical. Also better use i as variable name for an index.

Reported-by: kernel test robot <lkp@intel.com>
Suggested-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Link: https://lore.kernel.org/r/20220206023845.bpzxtjohekclffra@begin


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>