drm/amd/pm: fix smu i2c data read risk

commit d934e537

 upstream.

the smu driver_table is used for all types of smu
tables data transcation (e.g: PPtable, Metrics, i2c, Ecc..).

it is necessary to hold this lock to avoiding data tampering
during the i2c read operation.

Signed-off-by: Yang Wang <kevinyang.wang@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>