i2c: mux: demux-pinctrl: do not deactivate a master that is not active

Attempting to rollback the activation of the current master when
the current master has not been activated is bad. priv->cur_chan
and priv->cur_adap are both still zeroed out and the rollback
may result in attempts to revert an of changeset that has not been
applied and do result in calls to both del and put the zeroed out
i2c_adapter. Maybe it crashes, or whatever, but it's bad in any
case.

Fixes: e9d1a0a4 ("i2c: mux: demux-pinctrl: Fix an error handling path in 'i2c_demux_pinctrl_probe()'")
Signed-off-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Wolfram Sang <wsa@kernel.org>