drivers: usb: fix usb_dc_ep_mps() for the SAM0 for IN endpoints
drivers: usb: fix usb_dc_ep_mps() for the SAM0 for IN endpoints

The driver was returning zero due to accessing the, say, 0x81'th
endpoint instead of the 0x01'th endpoint.

Signed-off-by: Michael Hope <c71d7810e3c04e4d6ad9df326b82536b86a1bfbc@google.com>

Vudentz/zephyr,nashif/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,finikorg/zephyr,Vudentz/zephyr,nashif/zephyr,galak/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,finikorg/zephyr,Vudentz/zephyr,galak/zephyr,nashif/zephyr,finikorg/zephyr,finikorg/zephyr,galak/zephyr,nashif/zephyr,Vudentz/zephyr,Vudentz/zephyr