mfd: lp3943: Drop #include <linux/pwm.h> from header

The header doesn't make use of any symbols declared in <linux/pwm.h>.
There are tree files that #include <mfd/lp3943.h>. Two of them
(i.e. drivers/gpio/gpio-lp3943.c and drivers/mfd/lp3943.c) also don't
use any and the third (drivers/pwm/pwm-lp3943.c) has an explicit include
of <linux/pwm.h> itself.

So drop the unused include. The intended side effect is that
drivers/gpio/gpio-lp3943.c and drivers/mfd/lp3943.c stop importing the
"PWM" module namespace.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Link: https://lore.kernel.org/r/20250212170403.36619-2-u.kleine-koenig@baylibre.com
Signed-off-by: Lee Jones <lee@kernel.org>