devtools: fix symbol map change check

devtools: fix symbol map change check

Fix check symbol change script to detect new diff file when
it is in between  "--- /dev/null" to "b/lib/...".
Current awk line expects line to start with "a/..."
which is not always true for all diffs.
As a result if in_map was '1' earlier, it will not be changed
to '0' and we get check patch errors which are not true.

Fixes: 4bec48184e33 ("devtools: add checks for ABI symbol addition")
Cc: stable@dpdk.org
Signed-off-by: David Marchand <david.marchand@redhat.com>
Signed-off-by: Nithin Dabilpuram <ndabilpuram@marvell.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Tested-by: Jerin Jacob <jerinj@marvell.com>