pwm: omap-dmtimer: Simplify error handling

Instead of doing error handling in the middle of ->probe(), move error
handling and freeing the reference to timer to the end.

This fixes a resource leak as dm_timer wasn't freed when allocating
*omap failed.

Implementation note: The put: label was never reached without a goto and
ret being unequal to 0, so the removed return statement is fine.

Fixes: 6604c655 ("pwm: Add PWM driver for OMAP using dual-mode timers")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>