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.
bootloaders: uint32_t -> uintptr_t