Do not initialize variable if value is never read
hmc5883: Support for three sensors
mpu6000: Support for up to three accels / gyros
L3GD20: Support for up to three gyros
uORB: Support up to three topics per sensor
sdlog2: Add support for up to three IMU sensors
drivers: Up to three units support
Build fixes for example
sensors: Support for up to three sensors of the IMU types