spi/imx: simplify error handling to free gpios

Simplify the error handling by moving the code to free gpios in one place.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>