drm/panfrost: Skip speed binning on EOPNOTSUPP

Encountered on an ARM Mali-T760 MP4, attempting to read the nvmem
variable can also return EOPNOTSUPP instead of ENOENT when speed
binning is unsupported.

Cc: <stable@vger.kernel.org>
Fixes: 7d690f9 ("drm/panfrost: Add basic support for speed binning")
Signed-off-by: David Michael <fedora.dm0@gmail.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Signed-off-by: Steven Price <steven.price@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/87msyryd7y.fsf@gmail.com

Author: dm0-

drivers/gpu/drm/panfrost/panfrost_devfreq.c

@@ -96,7 +96,7 @@ static int panfrost_read_speedbin(struct device *dev)
 		 * keep going without it; any other error means that we are
 		 * supposed to read the bin value, but we failed doing so.
 		 */
-		if (ret != -ENOENT) {
+		if (ret != -ENOENT && ret != -EOPNOTSUPP) {
 			DRM_DEV_ERROR(dev, "Cannot read speed-bin (%d).", ret);
 			return ret;
 		}