CBD-1386:  fix PKG_SRC location

Change-Id: I91c1da5ea49787bd5a4ec29f2ba2862b02e23260
Reviewed-on: http://review.couchbase.org/39194
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>