drivers/misc/pch_phub.c: don't oops if dmi_get_system_info returns NULL

If dmi_get_system_info() returns NULL, pch_phub_probe() will dereferencea
a zero pointer.

This oops was observed on an Atom based board which has no BIOS, but a
bootloder which doesn't privde DMI data.
Signed-off-by: NAlexander Stein <alexander.stein@systec-electronic.com>
Cc: Tomoya MORINAGA <tomoya-linux@dsn.okisemi.com>
Cc: Greg KH <gregkh@suse.de>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

drivers/misc/pch_phub.c

@@ -686,6 +686,8 @@ static int __devinit pch_phub_probe(struct pci_dev *pdev,
 	}
 
 	if (id->driver_data == 1) { /* EG20T PCH */
+		const char *board_name;
+
 		retval = sysfs_create_file(&pdev->dev.kobj,
 					   &dev_attr_pch_mac.attr);
 		if (retval)
@@ -701,7 +703,8 @@ static int __devinit pch_phub_probe(struct pci_dev *pdev,
 					       CLKCFG_CANCLK_MASK);
 
 		/* quirk for CM-iTC board */
-		if (strstr(dmi_get_system_info(DMI_BOARD_NAME), "CM-iTC"))
+		board_name = dmi_get_system_info(DMI_BOARD_NAME);
+		if (board_name && strstr(board_name, "CM-iTC"))
 			pch_phub_read_modify_write_reg(chip,
 						(unsigned int)CLKCFG_REG_OFFSET,
 						CLKCFG_UART_48MHZ | CLKCFG_BAUDDIV |