dsp: fix dangling pointer access

Assign the circular buffer address to port buffer only after ION
allocation is succesful to fix dangling pointer access.
Also, lock the circular buffer memory allocation in order to
avoid multiple allocations for a port.

CRs-Fixed: 2096407
Change-Id: I22c1d55ea611ac59cdca51924787f6831bad8c2b
Signed-off-by: Aditya Bavanari <abavanar@codeaurora.org>