usb: host: max3421-hcd: fix mask of IO control register

GPIO control register is divided into IOPINS1 and IOPINS2.
And low 4-bit of register is controls output.

So, this patch fixes wrong mask of GPIO output.

Signed-off-by: Jaewon Kim <jaewon02.kim@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>