pwm: Fix pwm_apply_args()

Commit 5ec803ed ("pwm: Add core infrastructure to allow atomic
updates"), implemented pwm_disable() as a wrapper around
pwm_apply_state(), and then, commit ef2bf499 ("pwm: Improve args
checking in pwm_apply_state()") added missing checks on the ->period
value in pwm_apply_state() to ensure we were not passing inappropriate
values to the ->config() or ->apply() methods.

The conjunction of these 2 commits led to a case where pwm_disable()
was no longer succeeding, thus preventing the polarity setting done
in pwm_apply_args().

Set a valid period in pwm_apply_args() to ensure polarity setting
won't be rejected.

Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Suggested-by: Brian Norris <briannorris@chromium.org>
Fixes: 5ec803ed ("pwm: Add core infrastructure to allow atomic updates")
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>