spi/bcm63xx: Fix checkpatch warnings

This patch fixes the checkpatch.pl warnings on the driver
file.

Signed-off-by: Aravind Thokala <aravind.thk@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>