drm/vc4: hdmi: Fix off by ones in vc4_hdmi_read/write()

The variant->registers[] has ->num_registers elements so the >
comparison needs to be changes to >= to prevent an out of bounds
access.

Fixes: 311e305f ("drm/vc4: hdmi: Implement a register layout abstraction")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20200910100748.GA79916@mwanda

drivers/gpu/drm/vc4/vc4_hdmi_regs.h

@@ -398,7 +398,7 @@ static inline u32 vc4_hdmi_read(struct vc4_hdmi *hdmi,
 	const struct vc4_hdmi_variant *variant = hdmi->variant;
 	void __iomem *base;
 
-	if (reg > variant->num_registers) {
+	if (reg >= variant->num_registers) {
 		dev_warn(&hdmi->pdev->dev,
 			 "Invalid register ID %u\n", reg);
 		return 0;
@@ -424,7 +424,7 @@ static inline void vc4_hdmi_write(struct vc4_hdmi *hdmi,
 	const struct vc4_hdmi_variant *variant = hdmi->variant;
 	void __iomem *base;
 
-	if (reg > variant->num_registers) {
+	if (reg >= variant->num_registers) {
 		dev_warn(&hdmi->pdev->dev,
 			 "Invalid register ID %u\n", reg);
 		return;