phy: cadence: Sierra: Fix build warning

Variable "sp" is not used so remove it.

Fixes: 5311ca8aa824 ("phy: cadence: Sierra: add phy_reset hook")
Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>

drivers/phy/cadence/phy-cadence-sierra.c

@@ -335,7 +335,6 @@ static int cdns_sierra_phy_on(struct phy *gphy)
 static int cdns_sierra_phy_off(struct phy *gphy)
 {
 	struct cdns_sierra_inst *ins = phy_get_drvdata(gphy);
-	struct cdns_sierra_phy *sp = dev_get_drvdata(gphy->dev.parent);
 
 	return reset_control_assert(ins->lnk_rst);
 }