ptp: ocp: Fix a couple NULL vs IS_ERR() checks

The ptp_ocp_get_mem() function does not return NULL, it returns error
pointers.

Fixes: 773bda964921 ("ptp: ocp: Expose various resources on the timecard.")
Signed-off-by: Dan Carpenter <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/ptp/ptp_ocp.c

···
 	if (!ext)
 		return -ENOMEM;
 
-	err = -EINVAL;
 	ext->mem = ptp_ocp_get_mem(bp, r);
-	if (!ext->mem)
+	if (IS_ERR(ext->mem)) {
+		err = PTR_ERR(ext->mem);
 		goto out;
+	}
 
 	ext->bp = bp;
 	ext->info = r->extra;
···
 	void __iomem *mem;
 
 	mem = ptp_ocp_get_mem(bp, r);
-	if (!mem)
-		return -EINVAL;
+	if (IS_ERR(mem))
+		return PTR_ERR(mem);
 
 	bp_assign_entry(bp, r, mem);