If disabling interconnects fails there's not a lot we can do.  The
only two callers of ipa_interconnect_disable() ignore the return
value, so just give the function a void return type.

Print an error message if disabling any of the interconnects is not
successful.  Return (and print) only the first error seen.
Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>