We can use iopoll for checking the EOCZ (end of conversion) bit. And with
this we now also want to handle the timeout errors properly.

For omap3, we need about 1.2ms for the single mode sampling to wait for
EOCZ down, so let's use 1.5ms timeout there. Waiting for sampling to start
is faster and we can use 1ms timeout.

Cc: Adam Ford <aford173@gmail.com>
Cc: Carl Philipp Klemm <philipp@uvos.xyz>
Cc: Eduardo Valentin <edubezval@gmail.com>
Cc: H. Nikolaus Schaller <hns@goldelico.com>
Cc: Merlijn Wajer <merlijn@wizzup.org>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Peter Ujfalusi <peter.ujfalusi@gmail.com>
Cc: Sebastian Reichel <sre@kernel.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Tested-by: Adam Ford <aford173@gmail.com> #logicpd-torpedo-37xx-devkit
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20210205134534.49200-4-tony@atomide.com