pipeline: fix build with GCC 4.8.5

pipeline: fix build with GCC 4.8.5

Compilation on CentOS 7 with gcc version 4.8.5 fails with
the following errors:
error: 'src_struct_id' may be used uninitialized in this
function [-Werror=maybe-uninitialized]
error: 'dst_struct_id' may be used uninitialized in this
function [-Werror=maybe-uninitialized]

This patch fixes the build errors by initializing both variables.

Bugzilla ID: 683
Fixes: 783768136f29 ("pipeline: auto-detect endianness of action arguments")

Signed-off-by: Ali Alnubani <alialnu@nvidia.com>