freertos: Fix save_context. Add RSYNC after WSR
freertos: Fix save_context. Add RSYNC after WSR

RSYNC waits for all previously fetched WSR.* instructions to be performed before inter-
preting the register fields of the next instruction.

espressif/esp-idf,espressif/esp-idf,espressif/esp-idf,espressif/esp-idf