net: phy: mscc: macsec: fix sparse warnings

This patch fixes the following sparse warnings when building MACsec
support in the MSCC PHY driver.

  mscc_macsec.c:393:42: warning: cast from restricted sci_t
  mscc_macsec.c:395:42: warning: restricted sci_t degrades to integer
  mscc_macsec.c:402:42: warning: restricted __be16 degrades to integer
  mscc_macsec.c:608:34: warning: cast from restricted sci_t
  mscc_macsec.c:610:34: warning: restricted sci_t degrades to integer

Signed-off-by: Antoine Tenart <antoine.tenart@bootlin.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>