fixup! overlays: mcp23017: allow specification of the i2c bus #921

Job	Run time
build (bcm2835, arm, bcm2835_defconfig, kernel)	14m 4s
build (arm64, arm64, defconfig, kernel8)	45m 26s
build (bcmrpi, arm, bcmrpi_defconfig, kernel)	55m 54s
build (bcm2709, arm, bcm2709_defconfig, kernel7)	52m 50s
build (bcm2711, arm, bcm2711_defconfig, kernel7l)	43m 42s
build (bcm2711_arm64, arm64, bcm2711_defconfig, kernel8)	1h 14m 53s
build (bcm2712, arm64, bcm2712_defconfig, kernel_2712)	1h 9m 42s
	5h 56m 31s

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