drm/i915: Use unsigned long for obj->user_pin_count

At least on linux sizeof(long) == sizeof(void*) and the thinking
is that you can grab about as many references as there's memory.

Doesn't really matter, just a bit of OCD since the fixed size data
type in a pure in-kernel datastructure look off.

v2: Ville asked for an overflow check since no one prevents userspace
from incrementing the pin count forever.

v3: s/INT/LONG/, noticed by Chris.

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.h

@@ -1604,7 +1604,7 @@ struct drm_i915_gem_object {
 	unsigned long *bit_17;
 
 	/** User space pin count and filp owning the pin */
-	uint32_t user_pin_count;
+	unsigned long user_pin_count;
 	struct drm_file *pin_filp;
 
 	/** for phy allocated objects */

drivers/gpu/drm/i915/i915_gem.c

@@ -3931,6 +3931,11 @@ i915_gem_pin_ioctl(struct drm_device *dev, void *data,
 		goto out;
 	}
 
+	if (obj->user_pin_count == ULONG_MAX) {
+		ret = -EBUSY;
+		goto out;
+	}
+
 	if (obj->user_pin_count == 0) {
 		ret = i915_gem_obj_ggtt_pin(obj, args->alignment, true, false);
 		if (ret)