pios tcp/udp: uint32_t -> uintptr_t
pios usart: uint32_t -> uintptr_t
pios rfm22b_com: uint32_t -> uintptr_t
pios usb: uint32_t -> uintptr_t
pios com_msg: uint32_t -> uintptr_t
pios usb_rctx: uint32_t -> uintptr_t
pios can: uint32_t -> uintptr_t
pios dsm: uint32_t -> uintptr_t
pios pwm: uint32_t -> uintptr_t
pios ppm: uint32_t -> uintptr_t
pios sbus: uint32_t -> uintptr_t
pios rcvr: uint32_t -> uintptr_t
pios gcsrcvr: uint32_t -> uintptr_t
Telemetry: uint32_t -> uintptr_t
TransmitterControl: cast error codes to uint16_t

The channels are uint16_t and the constant return codes are
negative which creates a compiler warning about always false.
This casts the values to make them wrap around.

Alternatively we could make ManualControlCommand channels int16_t
TransmitterControl: uint32_t -> uintptr_t
pios servo: uint32_t -> uintptr_t
pios overo: uint32_t -> uintptr_t
firmware: uint32_t -> uintpr_t
sim: uint32_t -> uintptr_t

This is for consistency with the flight code.