staging: comedi: me4000: use comedi_timeout() to wait for ai (*insn_read)

Use the comedi_timeout() helper to busy-wait for the analog input end-of-
conversion instead of the udelay().

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>