mfd: axp20x: Fix axp288 PEK_DBR and PEK_DBF irqs being swapped

The R in PEK_DBR stands for rising, so it should be mapped to
AXP288_IRQ_POKP where the last P stands for positive edge.

Likewise PEK_DBF should be mapped to the falling edge, aka the
_N_egative edge, so it should be mapped to AXP288_IRQ_POKN.

This fixes the inverted powerbutton status reporting by the
axp20x-pek driver.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>