net: hisilicon: include linux/vmalloc.h in dsaf

Some configurations fail to build the hns dsaf code because of
a missing header file:

ethernet/hisilicon/hns/hns_dsaf_main.c: In function 'hns_dsaf_init':
ethernet/hisilicon/hns/hns_dsaf_main.c:1096:2: error: implicit declaration of function 'vzalloc' [-Werror=implicit-function-declaration]
  priv->soft_mac_tbl = vzalloc(sizeof(*priv->soft_mac_tbl)

This adds the correct #include.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>