drm/amd/pm: Use devm_i2c_add_adapter() in the Sienna smu

drm/amd/pm: Use devm_i2c_add_adapter() in the Sienna smu

The I2C init for Sienna Cichlid uses i2c_add_adapter() and
i2c_del_adapter(), this commit replaces the use of these two functions
with devm_i2c_add_adapter(). Notice that Sienna Cichlid init initializes
multiple I2C buses in a loop; if something goes wrong, the previous
adapters are removed, and the amdgpu load is interrupted. Since I2C init
is required for the correct load of amdgpu, it is safe to rely on
devm_i2c_add_adapter() to handle any previously initialized I2C adapter.

Signed-off-by: Rodrigo Siqueira <siqueira@igalia.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>