gpio: dwapb: Drop redundant check in dwapb_irq_set_type()

For more than 15 years we may not get into ->irq_set_type()
without any meaningful type provided.

Drop redundant check in dwapb_irq_set_type().

See the commit e76de9f8 ("[PATCH] genirq: add SA_TRIGGER support")
out of curiosity.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>