i2c: pca-platform: Use platform_irq_get_optional

i2c: pca-platform: Use platform_irq_get_optional

BugLink: https://bugs.launchpad.net/bugs/1873481
[ Upstream commit 14c1fe699cad9cb0acda4559c584f136d18fea50 ]

The interrupt is not required so use platform_irq_get_optional() to
avoid error messages like

  i2c-pca-platform 22080000.i2c: IRQ index 0 not found

Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Kelsey Skunberg <kelsey.skunberg@canonical.com>