msm: dcvs: allow re-registration of cores

If a core has already been registered with dcvs, just
return the previous dcvs core id if it is registered
again.

Change-Id: Ida34a2145c21b17f39499eb81dfd4ccd17f6e56d
Signed-off-by: Steve Muckle <smuckle@codeaurora.org>