gpio: tegra186: remove unneeded loop in tegra186_gpio_init_route_mapping()

Reviewing the j loop over num_irqs_per_bank, in the code previous
to the fixes: commit, every j was used. now only when j == 0.
If only j == 0 is used, there is no need for the loop.

Fixes: 21038680 ("gpio: tegra186: Support multiple interrupts per bank")
Signed-off-by: Tom Rix <trix@redhat.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>