GPIO: gpio-generic: remove kfree() from bgpio_remove call

Memory for basic-mmio-gpio driver is allocated by the driver
using it, whether it's the generic GPIO driver itself or another
driver. In either case, the owner shall allocate and free the
struct bgpio_chip it is using, preferably using a managed
resource.

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>