i2c: omap: Improve error reporting for problems during .remove()

If pm_runtime_get() fails in .remove() the driver used to return the
error to the driver core. The only effect of this (compared to returning
zero) is a generic warning that the error value is ignored.

So emit a better warning and return zero to suppress the generic (and
little helpful) message. Also disable runtime PM in the error case.

This prepares changing platform device remove callbacks to return void.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>