drm/amd/display: Don't re-enable CRC when CONFIG_DEBUG_FS isn't defined

[Why]
When CONFIG_DEBUG_FS isn't defined then amdgpu_dm_crtc_set_crc_source
is NULL. This causes a compilation error since it's being called
unconditionally.

[How]
Guard the call based on CONFIG_DEBUG_FS - CRC capture isn't supported
without this.

Cc: Leo Li <sunpeng.li@amd.com>
Cc: Harry Wentland <harry.wentland@amd.com>
Fixes: 43a6a02e ("drm/amd/display: Re-enable CRC capture following modeset")
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>