spi: pxa2xx: Use gpiod_put() not gpiod_free()

gpiod_free() is an internal function for gpiolib, gpiod_put() is the
correct external function.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Suggested-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Mark Brown <broonie@kernel.org>