i2c: core: Dispose OF IRQ mapping at client removal time

Clients instantiated from OF get an IRQ mapping created at device
registration time. Dispose the mapping when the client is removed.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Cc: stable@kernel.org