gps: use an inline function for usleep instead of #define
gps: use an inline function for usleep instead of #define

This avoids conflicts with other code

CornerOfSkyline/qgroundcontrol,RedoXyde/PX4_qGCS,CornerOfSkyline/qgroundcontrol,Hunter522/qgroundcontrol,RedoXyde/PX4_qGCS,CornerOfSkyline/qgroundcontrol,ethz-asl/qgc_asl,RedoXyde/PX4_qGCS,Hunter522/qgroundcontrol,CornerOfSkyline/qgroundcontrol,Hunter522/qgroundcontrol,CornerOfSkyline/qgroundcontrol,Hunter522/qgroundcontrol,kd0aij/qgroundcontrol,ethz-asl/qgc_asl,RedoXyde/PX4_qGCS,Hunter522/qgroundcontrol,ethz-asl/qgc_asl,kd0aij/qgroundcontrol,CornerOfSkyline/qgroundcontrol,kd0aij/qgroundcontrol,RedoXyde/PX4_qGCS,kd0aij/qgroundcontrol,kd0aij/qgroundcontrol,ethz-asl/qgc_asl,kd0aij/qgroundcontrol,Hunter522/qgroundcontrol,RedoXyde/PX4_qGCS,ethz-asl/qgc_asl