xtensa: fix warning comparing pointer to 0

Fix the following coccicheck warning:

./arch/xtensa/kernel/pci.c:79:17-18: WARNING comparing pointer to 0.
Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Message-Id: <1615360238-22508-1-git-send-email-jiapeng.chong@linux.alibaba.com>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

arch/xtensa/kernel/pci.c

@@ -76,7 +76,7 @@ int pci_iobar_pfn(struct pci_dev *pdev, int bar, struct vm_area_struct *vma)
 	struct pci_controller *pci_ctrl = (struct pci_controller*) pdev->sysdata;
 	resource_size_t ioaddr = pci_resource_start(pdev, bar);
 
-	if (pci_ctrl == 0)
+	if (!pci_ctrl)
 		return -EINVAL;		/* should never happen */
 
 	/* Convert to an offset within this PCI controller */