rp2/mpthreadport.h: Cast core_state to _mp_state_thread_t.
rp2/mpthreadport.h: Cast core_state to _mp_state_thread_t.

Required for user C++ code to build successfully against ports/rp2.

Signed-off-by: Phil Howard <e888d2bd6f13f82caa51a37c03d034c76f661ba3@pimoroni.com>

pfalcon/micropython,pfalcon/micropython,pfalcon/micropython,pfalcon/micropython,pfalcon/micropython