drm/amd/pm: fix smu_v11_0_init_power power_context allocation

Allocate smu_power->power_context to size of smu_11_0_power_context instead of
smu_11_0_dpm_context.

Signed-off-by: Ryan Taylor <Ryan.Taylor@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>