drm/amd: Remove needless break for legacy IP discovery MP0 9.0.0

There is already a "default" case in the switch block, so there is
no need to have a break after the switch block.

Reviewed-by: Aaron Liu <aaron.liu@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>