pinctrl: imx: fix memory leak

Each time set_state is called, a new piece memory will
be allocated for pin_data, but not freed, this will
incur memory leak.

When error, the devm API could not free memory automatically.
So need call devm_kfree when error.

Issue reported by Coverity

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Cc: Simon Glass <sjg@chromium.org>
Cc: Stefan Agner <stefan.agner@toradex.com>
Cc: Stefano Babic <sbabic@denx.de>