mm-audio: Remove malloc allocation for ptr pointer

Currently free of ptr pointer is failing because
ptr pointer is not pointing to base address of malloc
function. Reason is, strtoul api stores the address
of the first invalid character of input string parameter
to ptr pointer. Hence removing malloc allocation is not
required as value of ptr pointer will be first invalid
input string address.

Change-Id: I612002b15594b666bf9053c3e49bc62a7efb86ee