FALCON_SPI_MAX_LEN has type size_t while other SPI lengths have type
unsigned int. This results in warnings from min() on 64-bit
architectures where they are different. Add a cast to make it match.
From: Steve Hodgson <shodgson@solarflare.com>
Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>