Input: turbografx - store object in correct index

The variable i is used to check the port to attach to and we are
supposed to save the reference of struct tgfx in the location given by
tgfx_base[i]. But after finding out the index, i is getting modified
again so we saved in a wrong index.

Fixes: 4de27a63

 ("Input: turbografx - use parallel port device model")
Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>