pwm: tiehrpwm: add missing __iomem annotation

Fix the following sparse warnings:

drivers/pwm/pwm-tiehrpwm.c:144:16: warning: incorrect type in argument 1 (different address spaces)
drivers/pwm/pwm-tiehrpwm.c:144:16:    expected void const volatile [noderef] <asn:2>*addr
drivers/pwm/pwm-tiehrpwm.c:144:16:    got void *
drivers/pwm/pwm-tiehrpwm.c:149:9: warning: incorrect type in argument 2 (different address spaces)
drivers/pwm/pwm-tiehrpwm.c:149:9:    expected void volatile [noderef] <asn:2>*addr
drivers/pwm/pwm-tiehrpwm.c:149:9:    got void *
drivers/pwm/pwm-tiehrpwm.c:157:18: warning: incorrect type in argument 1 (different address spaces)
drivers/pwm/pwm-tiehrpwm.c:157:18:    expected void const volatile [noderef] <asn:2>*addr
drivers/pwm/pwm-tiehrpwm.c:157:18:    got void *
drivers/pwm/pwm-tiehrpwm.c:160:9: warning: incorrect type in argument 2 (different address spaces)
drivers/pwm/pwm-tiehrpwm.c:160:9:    expected void volatile [noderef] <asn:2>*addr
drivers/pwm/pwm-tiehrpwm.c:160:9:    got void *

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>