soc/tegra: pmc: Change powergate and rail IDs to be an unsigned type

The Tegra powergate and rail IDs are always positive values and so change
the type to be unsigned and remove the tests to see if the ID is less
than zero. Update the Tegra DC powergate type to be an unsigned as well.

Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>

drivers/gpu/drm/tegra/drm.h

@@ -121,7 +121,7 @@ struct tegra_dc {
 	spinlock_t lock;
 
 	struct drm_crtc base;
-	int powergate;
+	unsigned int powergate;
 	int pipe;
 
 	struct clk *clk;