hwmon: (pmbus/adm1266) serialize sequencer_state debugfs read with pmbus_lock

hwmon: (pmbus/adm1266) serialize sequencer_state debugfs read with pmbus_lock

adm1266_state_read() backs the sequencer_state debugfs entry and
issues an i2c_smbus_read_word_data(client, ADM1266_READ_STATE)
against the device without taking pmbus_lock.  pmbus_core holds
pmbus_lock around its own multi-transaction sequences (notably the
"set PAGE, then read paged register" pattern used by hwmon
attributes), so an unlocked debugfs reader can land between a PAGE
write and the subsequent paged read in another thread.  READ_STATE
itself is not paged, so it cannot corrupt PAGE in flight, but the
same defensive serialisation that applies to the GPIO accessors
applies here: any direct device access from outside pmbus_core
should be ordered with respect to pmbus_core's own.

Take pmbus_lock at the top of adm1266_state_read() via the
scope-based guard().

Fixes: ed1ff457e187 ("hwmon: (pmbus/adm1266) add debugfs for states")
Cc: stable@vger.kernel.org
Signed-off-by: Abdurrahman Hussain <abdurrahman@nexthop.ai>
Link: https://lore.kernel.org/r/20260518-adm1266-gpio-fixes-v3-8-e425e4f88139@nexthop.ai
Signed-off-by: Guenter Roeck <linux@roeck-us.net>