i40e: fix flow director index sign

i40e: fix flow director index sign

Coverity issue reported like
CID 119268 (#1 of 1): Unintended sign extension
(SIGN_EXTENSION)sign_extension: Suspicious implicit sign extension:
vsi_id with type unsigned short (16 bits, unsigned) is promoted in
vsi_id << 23 to type int (32 bits, signed), then sign-extended to type
unsigned long (64 bits, unsigned). If vsi_id << 23 is greater than
0x7FFFFFFF, the upper bits of the result will all be 1.

Fixes: 88ebc2b7f976 ("i40e: extend flow director to support VF")
Signed-off-by: Jingjing Wu <jingjing.wu@intel.com>
Acked-by: John McNamara <john.mcnamara@intel.com>