drm/amd/display: Remove incorrect FP context start

All the DC_FP_START/END should be used before call anything from DML2,
for this reason, the use of those guards inside DML it is not correct.
This commit removes two unnecessary DC_FP_START/END from a dml2
function.

Reviewed-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>