drm/amdgpu: Specify get_argument function for ci_smu_funcs

Starting in Linux 5.8, the graphics and memory clock frequency were not being
reported for CIK cards. This is a regression, since they were reported correctly
in Linux 5.7.

After investigation, I discovered that the smum_send_msg_to_smc() function,
attempts to call the corresponding get_argument() function of ci_smu_funcs.
However, the get_argument() function is not defined in ci_smu_funcs.

This patch fixes the bug by specifying the correct get_argument() function.

Fixes: a0ec2256 ("drm/amd/powerplay: unified interfaces for message issuing and response checking")
Signed-off-by: Sandeep Raghuraman <sandy.8925@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>