raspberrypi3-64.conf: Don't use raspberrypi as MACHINEOVERRIDES
The current setup broke the build for rpi3-64 when we wanted to port
some changes from rpi3 to rpi0.
#@NAME: RaspberryPi 3 Development Board
#@DESCRIPTION: Machine configuration for the RaspberryPi 3 in 64 bits mode
-MACHINEOVERRIDES = "raspberrypi3:raspberrypi:${MACHINE}"
+MACHINEOVERRIDES = "raspberrypi3:${MACHINE}"
MACHINE_EXTRA_RRECOMMENDS += "linux-firmware-bcm43430"
