Free version buffer in the Vendor HAL's

XML parsing logic.

Fixes a minor memory leak that results from
not freeing that buffer.

Bug: 269520490
Test: Manual test
       1. Create several XML files under
          /vendor/etc/wifi/vendor_hals
       2. Modify the codepath to run the
          initVendorHalsDescriptorList method
	  (does not run by default on Pixel).
       3. Check that the XML parsing logic is
          working as intended.
Change-Id: I42944169b70c759998d94e8523d2aa55d0366ffd