drm/i915: Free write_buf that we allocated with kzalloc.

We use kzalloc to allocate the write_buf that we use for
i2c transfer on hdcp write. But it seems that we are forgetting
to free the memory that is not needed after i2c transfer is
completed.

Reported-by: Brian J Wood <[email protected]>
Fixes: 2320175 ("drm/i915: Implement HDCP for HDMI")
Cc: Ramalingam C <[email protected]>
Cc: Sean Paul <[email protected]>
Cc: Jani Nikula <[email protected]>
Cc: Rodrigo Vivi <[email protected]>
Cc: <[email protected]> # v4.17+
Signed-off-by: Rodrigo Vivi <[email protected]>
Reviewed-by: Chris Wilson <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]
(cherry picked from commit 62d3a8d)
Signed-off-by: Rodrigo Vivi <[email protected]>

Author: rodrigovivi

drivers/gpu/drm/i915/intel_hdmi.c

@@ -943,8 +943,12 @@ static int intel_hdmi_hdcp_write(struct intel_digital_port *intel_dig_port,
 
 	ret = i2c_transfer(adapter, &msg, 1);
 	if (ret == 1)
-		return 0;
-	return ret >= 0 ? -EIO : ret;
+		ret = 0;
+	else if (ret >= 0)
+		ret = -EIO;
+
+	kfree(write_buf);
+	return ret;
 }
 
 static