spi: rockchip: make spi_enable_chip take bool

The spi_enable_chip function takes a boolean
argument. Change the type to reflect that.

Signed-off-by: Emil Renner Berthing <kernel@esmil.dk>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Mark Brown <broonie@kernel.org>