can: ifi: Increment TX counters only on real transmission

can: ifi: Increment TX counters only on real transmission

Only increment the TX counters in the irq handler if a CAN message
was sent. The current code incremented the counters also if the TX
FIFO empty interrupt happened, which is incorrect.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Marc Kleine-Budde <mkl@pengutronix.de>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Oliver Hartkopp <socketcan@hartkopp.net>
Cc: Wolfgang Grandegger <wg@grandegger.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>