pinctrl: mediatek: Make eint_m u16

For SoC's which lacks EINT support, U16_MAX is assigned to both eint_m
and eint_n through macro NO_EINT_SUPPORT. This will generate integer
overflow warning because eint_m is declared as u8 type. Hence modify
the eint_m type to u16.

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>