pwm: tegra: Drop an if block with an always false condition

tegra_pwm_remove() is only called after tegra_pwm_probe() successfully
completed. In this case platform_set_drvdata() was called with a
non-NULL value and so platform_get_drvdata(pdev) cannot return NULL.

Returning an error code from a platform_driver's remove function is
ignored anyway, so it's a good thing this exit path is gone.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>