gpio: TS-4800: remove useless bgpio_init flags

No flags are required for bgpio_init in the TS-4800 gpio driver. This
patch set zero instead. The driver will have the same behaviour since
the & operator between the flags already resulted to zero.

Fixes: 5041e791 ("gpio: add TS-4800 fpga GPIO support")
Signed-off-by: Julien Grossholtz <julien.grossholtz@savoirfairelinux.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>