drivers: i2c_tca954x: Fix transfer function

This is a follow-up to commit e1c0a494.

The `tca954x_transfer()` function cannot call `i2c_transfer_dt()`,
because the I2C device address used in the transaction must be the one
passed as the `addr` parameter, not the address of the TCA954xA switch
itself. Hence, this commit restores the call to `i2c_transfer()`.

Signed-off-by: Andrzej Głąbek <andrzej.glabek@nordicsemi.no>