spi/bcm63xx: inline hz usage in bcm63xx_spi_setup_transfer

bcm63xx_spi_setup_transfer is called from only one place, and that has
t always set, to hz will always be t->speed_hz - just use it directly in
the two places instead of moving it in a local variable.

Signed-off-by: Jonas Gorski <jogo@openwrt.org>
Acked-by: Florian Fainelli <florian@openwrt.org>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>