drm/amd/display: Fix unused initialization of pointer sink

Pointer sink is being inintialized with a value that is never read,
it is later being re-assigned a new value. Remove the redundant
initialization.

Addresses-Coverity: ("Unused value")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>