gpiosim: initialize the bank's num_lines field to 1

gpiosim: initialize the bank's num_lines field to 1

If we create a simulated chip and never set the num_lines property, the
num_lines field remains set to 0 and the potential lineX and hog
directories within the bank's directory will not get removed so the
removal of the bank's and device's directories will fail too leaving
a dangling chip in place.

Initialize bank->num_lines to 1 to avoid this issue.

Fixes: a2f6e8cd3540 ("libgpiosim: new library for controlling the gpio-sim module")
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>