rockchip: spi: consistently use false/true with rkspi_enable_chip

While rkspi_enable_chip is called with true/false everywhere else in
the file, one call site uses '0' to denot 'false'.
This change this one parameter to 'false' and effects consistency.

Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>