drivers: i2c: i2c_dw: make target stop callback after read/write callbacks

In target mode, issue the stop callback from the I2C DW driver after the
read/write callbacks. This mirrors the behavior of other I2C target mode
drivers, and allows target handler code to correctly service any pending
read or write requests before it handles the stop condition.

Fixes #98675

Signed-off-by: Daniel DeGrasse <ddegrasse@tenstorrent.com>