i2c: core: Fix probing of i2c slaves without interrupts

Since commit 2fd36c55 ("i2c: core: Map OF IRQ at probe time"),
i2c slaves without interrupts (e.g. da9210 and at24 on r8a7791/koelsch)
fail to probe:

    at24: probe of 2-0050 failed with error -22

    da9210: probe of 6-0068 failed with error -22

This happens because the call to of_irq_get() in i2c_device_probe()
returns -EINVAL.

If a device node does not have an "interrupts" property,
of_irq_parse_one() fails. Unlike irq_of_parse_and_map(), of_irq_get()
does not ignore errors from of_irq_parse_one(), but forwards them.

Make i2c_device_probe() ignore all errors but -EPROBE_DEFER to fix this,
just like platform_get_irq() and platform_get_irq_byname() already do.

Fixes: 2fd36c55

 ("i2c: core: Map OF IRQ at probe time")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Tested-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>