net: freescale: ucc_geth: Return early when TBI PHY can't be found

In ucc_geth's .mac_config(), we configure the TBI Serdes block represented by a
struct phy_device that we get from firmware.

While porting to phylink, a check was missed to make sure we don't try
to access the TBI PHY if we can't get it. Let's add it and return early
in case of error

Reported-by: kernel test robot <[e-mail]>
Reported-by: Dan Carpenter <[e-mail]>
Closes: https://lore.kernel.org/r/[e-mail]/
Fixes: 53036aa8d031 ("net: freescale: ucc_geth: phylink conversion")
Signed-off-by: Maxime Chevallier <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

drivers/net/ethernet/freescale/ucc_geth.c

···
 			pr_warn("TBI mode requires that the device tree specify a tbi-handle\n");
 
 		tbiphy = of_phy_find_device(ug_info->tbi_node);
-		if (!tbiphy)
+		if (!tbiphy) {
 			pr_warn("Could not get TBI device\n");
+			return;
+		}
 
 		value = phy_read(tbiphy, ENET_TBI_MII_CR);
 		value &= ~0x1000;	/* Turn off autonegotiation */