net: fec: reduce spin lock time in fec_ptp_adjfreq

move below calculate out of spin lock section
	diff = fep->cc.mult;
	diff *= ppb;
	diff = div_u64(diff, 1000000000ULL);

diff is local variable and not neccesary in spin lock

Signed-off-by: Frank Li <Frank.Li@freescale.com>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/freescale/fec_ptp.c

@@ -145,6 +145,7 @@ static int fec_ptp_adjfreq(struct ptp_clock_info *ptp, s32 ppb)
 	u64 diff;
 	unsigned long flags;
 	int neg_adj = 0;
+	u32 mult = FEC_CC_MULT;
 
 	struct fec_enet_private *fep =
 	    container_of(ptp, struct fec_enet_private, ptp_caps);
@@ -154,22 +155,19 @@ static int fec_ptp_adjfreq(struct ptp_clock_info *ptp, s32 ppb)
 		neg_adj = 1;
 	}
 
+	diff = mult;
+	diff *= ppb;
+	diff = div_u64(diff, 1000000000ULL);
+
 	spin_lock_irqsave(&fep->tmreg_lock, flags);
 	/*
 	 * dummy read to set cycle_last in tc to now.
 	 * So use adjusted mult to calculate when next call
 	 * timercounter_read.
 	 */
 	timecounter_read(&fep->tc);
-	fep->cc.mult = FEC_CC_MULT;
-	diff = fep->cc.mult;
-	diff *= ppb;
-	diff = div_u64(diff, 1000000000ULL);
 
-	if (neg_adj)
-		fep->cc.mult -= diff;
-	else
-		fep->cc.mult += diff;
+	fep->cc.mult = neg_adj ? mult - diff : mult + diff;
 
 	spin_unlock_irqrestore(&fep->tmreg_lock, flags);