isdn: mISDN: Fix potential NULL pointer dereference of kzalloc

Allocating memory via kzalloc for phi may fail and causes a
NULL pointer dereference. This patch avoids such a scenario.
Signed-off-by: NAditya Pakki <pakki001@umn.edu>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/isdn/hardware/mISDN/hfcsusb.c

@@ -263,6 +263,9 @@ hfcsusb_ph_info(struct hfcsusb *hw)
 	int i;
 
 	phi = kzalloc(struct_size(phi, bch, dch->dev.nrbchan), GFP_ATOMIC);
+	if (!phi)
+		return;
+
 	phi->dch.ch.protocol = hw->protocol;
 	phi->dch.ch.Flags = dch->Flags;
 	phi->dch.state = dch->state;