can: janz-ican3: fix uninitialized variable warnings

Analysis of the code shows that the struct ican3_msg variable cannot be
used uninitialized. Error conditions are checked and the loop terminates
before calling the ican3_handle_message() function with an uninitialized
value.

Signed-off-by: Ira W. Snyder <iws@ovro.caltech.edu>
Acked-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>