intel_scu_ipcutil: underflow in scu_reg_access()

commit b1d353ad upstream.

"count" is controlled by the user and it can be negative.  Let's prevent
that by making it unsigned.  You have to have CAP_SYS_RAWIO to call this
function so the bug is not as serious as it could be.

Fixes: 5369c02d ('intel_scu_ipc: Utility driver for intel scu ipc')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Darren Hart <dvhart@linux.intel.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/platform/x86/intel_scu_ipcutil.c

@@ -52,7 +52,7 @@ struct scu_ipc_data {
 
 static int scu_reg_access(u32 cmd, struct scu_ipc_data  *data)
 {
-	int count = data->count;
+	unsigned int count = data->count;
 
 	if (count == 0 || count == 3 || count > 4)
 		return -EINVAL;