xen: xen-pciback: Replace GFP_ATOMIC with GFP_KERNEL in pcistub_init_device

pcistub_init_device() is never called in atomic context.

The call chain ending up at pcistub_init_device() is:
[1] pcistub_init_device() <- pcistub_seize() <- pcistub_probe()
[2] pcistub_init_device() <- pcistub_init_devices_late() <-
	xen_pcibk_init()
pcistub_probe() is only set as ".probe" in struct pci_driver.
xen_pcibk_init() is is only set as a parameter of module_init().
These functions are not called in atomic context.

Despite never getting called from atomic context,
pcistub_init_device() calls kzalloc() with GFP_ATOMIC,
which does not sleep for allocation.
GFP_ATOMIC is not necessary and can be replaced with GFP_KERNEL,
which can sleep and improve the possibility of sucessful allocation.

This is found by a static analysis tool named DCNS written by myself.
And I also manually check it.

Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

drivers/xen/xen-pciback/pci_stub.c

@@ -364,7 +364,7 @@ static int pcistub_init_device(struct pci_dev *dev)
 	 * here and then to call kfree(pci_get_drvdata(psdev->dev)).
 	 */
 	dev_data = kzalloc(sizeof(*dev_data) +  strlen(DRV_NAME "[]")
-				+ strlen(pci_name(dev)) + 1, GFP_ATOMIC);
+				+ strlen(pci_name(dev)) + 1, GFP_KERNEL);
 	if (!dev_data) {
 		err = -ENOMEM;
 		goto out;