qlge: avoid memcpy buffer overflow

gcc-8.0.0 (snapshot) points out that we copy a variable-length string
into a fixed length field using memcpy() with the destination length,
and that ends up copying whatever follows the string:

    inlined from 'ql_core_dump' at drivers/net/ethernet/qlogic/qlge/qlge_dbg.c:1106:2:
drivers/net/ethernet/qlogic/qlge/qlge_dbg.c:708:2: error: 'memcpy' reading 15 bytes from a region of size 14 [-Werror=stringop-overflow=]
  memcpy(seg_hdr->description, desc, (sizeof(seg_hdr->description)) - 1);

Changing it to use strncpy() will instead zero-pad the destination,
which seems to be the right thing to do here.

The bug is probably harmless, but it seems like a good idea to address
it in stable kernels as well, if only for the purpose of building with
gcc-8 without warnings.

Fixes: a61f8026 ("qlge: Add ethtool register dump function.")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/qlogic/qlge/qlge_dbg.c

@@ -724,7 +724,7 @@ static void ql_build_coredump_seg_header(
 	seg_hdr->cookie = MPI_COREDUMP_COOKIE;
 	seg_hdr->segNum = seg_number;
 	seg_hdr->segSize = seg_size;
-	memcpy(seg_hdr->description, desc, (sizeof(seg_hdr->description)) - 1);
+	strncpy(seg_hdr->description, desc, (sizeof(seg_hdr->description)) - 1);
 }
 
 /*