AP_GPS: resolve compilation problem with timeval #31519

Job	Run time
build (chibios, Durandal)	19m 41s
build (chibios, MatekF405)	18m 6s
build (chibios, KakuteF7)	16m 27s
build (chibios, MatekH743-bdshot)	20m 9s
build (chibios, Pixhawk1-1M)	17m 46s
build (chibios, MatekF405-CAN)	4m 28s
build (chibios, DrotekP3Pro)	4m 35s
build (chibios, Hitec-Airspeed)	5m 44s
build (chibios, f103-GPS)	5m 26s
build (disco, armhf)	16m 25s
	2h 8m 47s

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