Fix PlatformIO build

[maxgerhardt]

Defines USBD_MAX_POWER_MA as a static 250mA, which is correct for all the boards supported in platform-raspberrypi (aka, RaspberryPi Pico and Nano RP2040 Connect) in accordance to the generator code.

Fixes previous build failure if attempting to use the latest core.

In file included from C:\Users\Max\.platformio\packages\framework-arduinopico/pico-sdk/lib/tinyusb/src/tusb.h:65,
                 from C:\Users\Max\.platformio\packages\framework-arduinopico\cores\rp2040\RP2040USB.cpp:28:
C:\Users\Max\.platformio\packages\framework-arduinopico\cores\rp2040\RP2040USB.cpp: In function 'const uint8_t* tud_descriptor_configuration_cb(uint8_t)':
C:\Users\Max\.platformio\packages\framework-arduinopico\cores\rp2040\RP2040USB.cpp:209:118: error: 'USBD_MAX_POWER_MA' was not declared in this scope
  209 |             TUD_CONFIG_DESCRIPTOR(1, interface_count, USBD_STR_0, usbd_desc_len, TUSB_DESC_CONFIG_ATT_REMOTE_WAKEUP, USBD_MAX_POWER_MA)
      |                                                                                                                      ^~~~~~~~~~~~~~~~~

[earlephilhower]

Thanks!