drm/i915: update the firmware download URL

The old URL works but gives 301 Moved Permanently. Update.
Reviewed-by: NMichal Wajdeczko <michal.wajdeczko@intel.com>
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1489574966-27200-1-git-send-email-jani.nikula@intel.com

drivers/gpu/drm/i915/intel_csr.c

@@ -49,7 +49,7 @@ MODULE_FIRMWARE(I915_CSR_SKL);
 MODULE_FIRMWARE(I915_CSR_BXT);
 #define BXT_CSR_VERSION_REQUIRED	CSR_VERSION(1, 7)
 
-#define FIRMWARE_URL  "https://01.org/linuxgraphics/intel-linux-graphics-firmwares"
+#define FIRMWARE_URL  "https://01.org/linuxgraphics/downloads/firmware"