gpio: tb10x: Drop unneeded free_irq() call

Current code uses devm_request_irq() in .probe, so drop the unneeded
free_irq() call in .remove.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Acked-by: Christian Ruppert <christian.ruppert@alitech.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>