fix MATEKF405SE MAG_I2C_INSTANCE

[nerdCopter]

• fix MATEKF405SE by defining BARO and MAG correctly

• need backports to 0.3.x as well.

• NEEDS TESTERS, no one stepping up -- please test this zip and comment below or in #655 :

• EmuFlight_0.4.1_MATEKF405SE_Build_6cc68df4e.hex.zip

closes #655