i2c: core: fix reference leak in i2c_register_adapter()

The reference count of the device incremented in device_initialize() is
not decremented when device_add() fails. Add a put_device() call before
returning from the function.

This bug was found by an experimental static analysis tool that I am
developing.

Fixes: 60f68597 ("i2c: core: Setup i2c_adapter runtime-pm before calling device_add()")
Signed-off-by: Joe Hattori <joe@pf.is.s.u-tokyo.ac.jp>
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>