populate-volatile.sh: remove repeated leading slashes in TNAME
This avoids triple slashes in the generated /etc/volatile.cache to
reduce disk usage and in the output when verbose mode is enabled.
As all the paths for volatiles start with a slash, we can change
TNAME=${ROOT_DIR}/${TNAME} to TNAME=${ROOT_DIR}${TNAME}. To avoid
a double slash when ROOT_DIR is /, we strip the extra slash from
ROOT_DIR.
Signed-off-by: Jonathan Liu <net147@gmail.com> Signed-off-by: Saul Wold <sgw@linux.intel.com>
