When switching from a special function like SPI to an input or output,
there was a brief period after the function was disabled but before the
pin's I/O state was configured, in which the state would be poorly defined.
This fixes the problem by switching off the special function after fully
configuring the I/O state.
Fixes#10226.
Signed-off-by: Paul Grayson <pdg@alum.mit.edu>
b208cf23e2