can: m_can: m_can_open(): remove IRQF_TRIGGER_FALLING from request_threaded_irq()'s flags

The threaded IRQ handler is used for the tcan4x5x driver only. The IRQ pin of
the tcan4x5x controller is active low, so better not use IRQF_TRIGGER_FALLING
when requesting the IRQ. As this can result in missing interrupts.

Further, if the device tree specified the interrupt as "IRQ_TYPE_LEVEL_LOW",
unloading and reloading of the driver results in the following error during
ifup:

| irq: type mismatch, failed to map hwirq-31 for gpio@20a8000!
| tcan4x5x spi1.1: m_can device registered (irq=0, version=32)
| tcan4x5x spi1.1 can2: TCAN4X5X successfully initialized.
| tcan4x5x spi1.1 can2: failed to request interrupt

This patch fixes the problem by removing the IRQF_TRIGGER_FALLING from the
request_threaded_irq().

Fixes: f524f829b7 ("can: m_can: Create a m_can platform framework")
Cc: Dan Murphy <dmurphy@ti.com>
Cc: Sriram Dash <sriram.dash@samsung.com>
Cc: Pankaj Sharma <pankj.sharma@samsung.com>
Link: https://lore.kernel.org/r/20201127093548.509253-1-mkl@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/m_can/m_can.c

@@ -1653,7 +1653,7 @@ static int m_can_open(struct net_device *dev)
 		INIT_WORK(&cdev->tx_work, m_can_tx_work_queue);
 
 		err = request_threaded_irq(dev->irq, NULL, m_can_isr,
-					   IRQF_ONESHOT | IRQF_TRIGGER_FALLING,
+					   IRQF_ONESHOT,
 					   dev->name, dev);
 	} else {
 		err = request_irq(dev->irq, m_can_isr, IRQF_SHARED, dev->name,