irqdomain: i2c: Switch to irq_find_mapping()

irq_linear_revmap() is deprecated, so remove all its uses and supersede
them by an identical call to irq_find_mapping().

Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>
Cc: Peter Rosin <peda@axentia.se>
Cc: linux-i2c@vger.kernel.org
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>