remote: Fix the build by explicitly casting the obj pointer for xdr_free

remote: Fix the build by explicitly casting the obj pointer for xdr_free

For some reason, xdr_free uses char * instead of void * for its 2nd
argument which is passed to a custom free routine. Commit
dc54b3ec missed this detail which made the build fail on a number of
platforms. Fix it by explicitly casting the object pointer to char *
just like we do in other places throughout the code base.

Signed-off-by: Erik Skultety <eskultet@redhat.com>