staging: comedi: s626: use comedi_timeout() on remaining loops

There were just a handful of more while loops in this file that needed
timeouts, and this patch takes care of them.  One new callback is
introduced, and all of the proper comedi_timeout() calls are then used.
The return type of s626_i2c_handshake() has been changed from uint32_t to
int so that a negative error code from comedi_timeout() can be propagated
if necessary.

Signed-off-by: Chase Southwood <chase.southwood@yahoo.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>