ieee802154: ca8210: Remove stray gpiod_unexport() call

There is no gpiod_export() and gpiod_unexport() looks pretty much stray.
The gpiod_export() and gpiod_unexport() shouldn't be used in the code,
GPIO sysfs is deprecated. That said, simply drop the stray call.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-wpan/20230528140938.34034-1-andriy.shevchenko@linux.intel.com