pwm: Move pwm_capture() dummy to restore order

Move the dummy pwm_capture(), to make the declaration order of all
dummies to match the declaration order of the real functions.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>