drivers/net/ethernet/sfc/ptp.c: adjust duplicate test

Delete successive tests to the same location.  rc was previously tested and
not subsequently updated.  efx_phc_adjtime can return an error code, so the
call is updated so that is tested instead.

A simplified version of the semantic match that finds this problem is as
follows: (http://coccinelle.lip6.fr/)

// <smpl>
@s exists@
local idexpression y;
expression x,e;
@@

*if ( \(x == NULL\|IS_ERR(x)\|y != 0\) )
 { ... when forall
   return ...; }
... when != \(y = e\|y += e\|y -= e\|y |= e\|y &= e\|y++\|y--\|&y\)
    when != \(XT_GETPAGE(...,y)\|WMI_CMD_BUF(...)\)
*if ( \(x == NULL\|IS_ERR(x)\|y != 0\) )
 { ... when forall
   return ...; }
// </smpl>
Signed-off-by: NJulia Lawall <Julia.Lawall@lip6.fr>
Acked-by: NBen Hutchings <bhutchings@solarflare.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/sfc/ptp.c

@@ -1439,7 +1439,7 @@ static int efx_phc_settime(struct ptp_clock_info *ptp,
 
 	delta = timespec_sub(*e_ts, time_now);
 
-	efx_phc_adjtime(ptp, timespec_to_ns(&delta));
+	rc = efx_phc_adjtime(ptp, timespec_to_ns(&delta));
 	if (rc != 0)
 		return rc;