ata: libata-core: fix NULL pointer deref in ata_host_alloc_pinfo()

In an unlikely (and probably wrong?) case that the 'ppi' parameter of
ata_host_alloc_pinfo() points to an array starting with a NULL pointer,
there's going to be a kernel oops as the 'pi' local variable won't get
reassigned from the initial value of NULL. Initialize 'pi' instead to
'&ata_dummy_port_info' to fix the possible kernel oops for good...

Found by Linux Verification Center (linuxtesting.org) with the SVACE static
analysis tool.

Signed-off-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>

Author: Sergey Shtylyov

drivers/ata/libata-core.c

@@ -5462,15 +5462,15 @@ struct ata_host *ata_host_alloc_pinfo(struct device *dev,
 				      const struct ata_port_info * const * ppi,
 				      int n_ports)
 {
-	const struct ata_port_info *pi;
+	const struct ata_port_info *pi = &ata_dummy_port_info;
 	struct ata_host *host;
 	int i, j;
 
 	host = ata_host_alloc(dev, n_ports);
 	if (!host)
 		return NULL;
 
-	for (i = 0, j = 0, pi = NULL; i < host->n_ports; i++) {
+	for (i = 0, j = 0; i < host->n_ports; i++) {
 		struct ata_port *ap = host->ports[i];
 
 		if (ppi[j])