mfd: twl6040: Drop devm_free_irq of devm_ allocated irq

The devm_request_irq function allocates irq that is released
when a driver detaches. Thus, there is no reason to explicitly
call devm_free_irq in probe or remove functions.

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Lee Jones <lee.jones@linaro.org>