net/enetfec: fix const pointer in UIO filename parsing

net/enetfec: fix const pointer in UIO filename parsing

With latest glibc (Fedora Rawhide):
../drivers/net/enetfec/enet_uio.c: In function 'file_name_match_extract':
../drivers/net/enetfec/enet_uio.c:37:16: warning: assignment discards
	'const' qualifier from pointer target type [-Wdiscarded-qualifiers]
   37 |         substr = strstr(filename, match);
      |                ^

Fixes: b84fdd39638b ("net/enetfec: support UIO")
Cc: stable@dpdk.org
Signed-off-by: David Marchand <david.marchand@redhat.com>
Acked-by: Hemant Agrawal <hemant.agrawal@nxp.com>