sensors-detect: Detect graphics card in all cases

On recent kernels, the i2c bus may not be an immediate child of the
graphics device, instead there can be a drm class device in between.
Treat all drm class devices as graphics devices so that probing the
i2c bus is disabled by default as intended.

CHANGES

@@ -37,6 +37,7 @@ SVN HEAD
                   Document driver support for NCT7802Y
                   Add detection of NCT7904D
                   Add detection of IT8790E
+                  Fix graphics cards detection (#2386, #2392)
 
 3.3.5 "Happy Birthday Beddy" (2014-01-22)
   libsensors: Improve documentation of two functions

prog/detect/sensors-detect

@@ -3897,7 +3897,9 @@ sub get_pci_class
 	my ($subsystem, $class);
 
 	$subsystem = sysfs_device_subsystem($device);
-	return 0 unless defined $subsystem && $subsystem eq "pci";
+	return 0 unless defined $subsystem;
+	return 0x0300 if $subsystem eq "drm";	# Graphics card
+	return 0 unless $subsystem eq "pci";
 
 	$class = sysfs_device_attribute($device, "class");
 	return 0 unless defined $class;