gpio: tca642x: fix input subcommand for gpio banks > 0

The value of input pin for bank > 0 is always 0 for input subcommand.
The reason is that gpio_bank variable is computed only for invert and
output subcommands (it depends on number of arguments). The default
value of zero causes to shift the mask away for banks > 0.

Please note that info subcommand works as expected, because the input
pin values are accessed differently.

Fixes: 61c1775f ("gpio: tca642x: Add the tca642x gpio expander driver")
Cc: Dan Murphy <dmurphy@ti.com>
Signed-off-by: Tomas Novotny <tomas@novotny.cz>