can: ems_usb: fix coding style

This patch fixes the coding style issues introduced in commit:

    90cfde46 can: ems_usb: Fix possible tx overflow

Reported-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>