LibBladeRF: Handle bladeRFGet{Correction,Frequency} C ret err codes
LibBladeRF: Handle bladeRFGet{Correction,Frequency} C ret err codes

Handle possible negative C error codes upon action.

Signed-off-by: Edward O'Callaghan <117173807d5a49976a891944633465c0daea7f98@alterapraxis.com>

adamwalker/hlibBladeRF,victoredwardocallaghan/hlibBladeRF