buildtools: fix experimental symbols listing

buildtools: fix experimental symbols listing

The map-list-symbol.sh script displays the filename, section and symbol
names of map files.

Example:
$ buildtools/map-list-symbol.sh -S EXPERIMENTAL \
    lib/librte_ethdev/rte_ethdev_version.map |grep rte_mtr_create
lib/librte_ethdev/rte_ethdev_version.map EXPERIMENTAL rte_mtr_create

The experimental symbol check should only consider the symbol name.

Fixes: 3290ac14eb94 ("buildtools: detect discrepancies for experimental symbols")
Cc: stable@dpdk.org
Signed-off-by: David Marchand <david.marchand@redhat.com>
Tested-by: Andrew Rybchenko <arybchenko@solarflare.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>