drm/i915: Rename struct i915_power_well field data to id

Calling it data seems to imply arbitrary data can be associated with the
power well. However, that field is used for look ups and expected to be
unique, so rename it.
Signed-off-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/f3916c3c5bfa793b0fc870fd44007a3ff425194d.1475770848.git-series.ander.conselvan.de.oliveira@intel.com

drivers/gpu/drm/i915/i915_drv.h

@@ -1322,7 +1322,8 @@ struct i915_power_well {
 	/* cached hw enabled state */
 	bool hw_enabled;
 	unsigned long domains;
-	unsigned long data;
+	/* unique identifier for this power well */
+	unsigned long id;
 	const struct i915_power_well_ops *ops;
 };