ACPI: thinkpad-acpi: fix oops when a module parameter has no value

set_ibm_param() could OOPS with a NULL pointer derreference if one did not give
any values for a module parameter it handles.  This would, of course, cause all
sort of trouble for future modprobing and require a reboot to clean up
properly.

Fix it by returning -EINVAL if no values are given for the parameter, and also
avoid any nastyness from BUG_ON while at it.

How to reproduce: modprobe thinkpad-acpi brightness
Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Tested-by: Mike Kershaw <dragorn@kismetwireless.net>
Signed-off-by: Len Brown <len.brown@intel.com>

drivers/misc/thinkpad_acpi.c

@@ -4817,9 +4817,15 @@ static int __init set_ibm_param(const char *val, struct kernel_param *kp)
 	unsigned int i;
 	struct ibm_struct *ibm;
 
+	if (!kp || !kp->name || !val)
+		return -EINVAL;
+
 	for (i = 0; i < ARRAY_SIZE(ibms_init); i++) {
 		ibm = ibms_init[i].data;
-		BUG_ON(ibm == NULL);
+		WARN_ON(ibm == NULL);
+
+		if (!ibm || !ibm->name)
+			continue;
 
 		if (strcmp(ibm->name, kp->name) == 0 && ibm->write) {
 			if (strlen(val) > sizeof(ibms_init[i].param) - 2)