ewrk3: silence GCC warning

Building ewrk3.o triggers this GCC warning:
    drivers/net/ethernet/dec/ewrk3.c: In function '__check_irq':
    drivers/net/ethernet/dec/ewrk3.c:1915:1: warning: return from incompatible pointer type [enabled by default]

This can be trivially fixed by changing the 'irq' parameter from int to
byte (which is an alias for unsigned char for module parameters).

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: David S. Miller <davem@davemloft.net>