net: dsa: microchip: remove IRQF_TRIGGER_FALLING in request_threaded_irq

KSZ swithes used interrupts for detecting the phy link up and down.
During registering the interrupt handler, it used IRQF_TRIGGER_FALLING
flag. But this flag has to be retrieved from device tree instead of hard
coding in the driver, so removing the flag.

Fixes: ff319a64

 ("net: dsa: microchip: move interrupt handling logic from lan937x to ksz_common")
Reported-by: Christian Eggers <ceggers@arri.de>
Signed-off-by: Arun Ramadoss <arun.ramadoss@microchip.com>
Link: https://lore.kernel.org/r/20221213101440.24667-1-arun.ramadoss@microchip.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>