As of gcc 5.1.1 20150618 (Red Hat 5.1.1-4) the -Werror=maybe-uninitialized
check detects that 'snapname' in recv_incremental_replication() may not be
initialized. Explicitly initialize the variable to resolved the warning.
libzfs_sendrecv.c: In function ‘recv_incremental_replication’:
libzfs_sendrecv.c:2019:2: error: ‘snapname’ may be used uninitialized in
(void) snprintf(buf, sizeof (buf), "%s@%s", fsname, snapname);
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>