esp4: remove redundant initialization of pointer esph

Pointer esph is being assigned a value that is never read, esph is
re-assigned and only read inside an if statement, hence the
initialization is redundant and can be removed.

Cleans up clang warning:
net/ipv4/esp4.c:657:21: warning: Value stored to 'esph' during
its initialization is never read
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

net/ipv4/esp4.c

@@ -654,7 +654,7 @@ static void esp_input_restore_header(struct sk_buff *skb)
 static void esp_input_set_header(struct sk_buff *skb, __be32 *seqhi)
 {
 	struct xfrm_state *x = xfrm_input_state(skb);
-	struct ip_esp_hdr *esph = (struct ip_esp_hdr *)skb->data;
+	struct ip_esp_hdr *esph;
 
 	/* For ESN we move the header forward by 4 bytes to
 	 * accomodate the high bits.  We will move it back after