drm/radeon/dpm: fix spread spectrum setup (v2)

Need to check for engine and memory clock ss separately
and only enable dynamic ss if either of them are found.

This should fix systems which have a ss table, but do
not have entries for engine or memory.  On those systems
we may enable dynamic spread spectrum without enabling
it on the engine or memory clocks which can lead to a
hang in some cases.

fixes some systems reported here:
https://bugs.freedesktop.org/show_bug.cgi?id=66963



v2: fix typo

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>