drm/i915/cnl: Fix aux selection for WA 1178

Current code always select _CNL_AUX_ANAOVRD1_B
register regardless the pw in use.

CNL_DISP_PW_AUX_B = 9
CNL_DISP_PW_AUX_C = 10
CNL_DISP_PW_AUX_D = 11

And for pick we want

B = 0
C = 1
D = 2

Fixes: ddd39e4b ("drm/i915/cnl: apply Display WA #1178 to fix type C dongles")
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Acked-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180123215245.24026-1-rodrigo.vivi@intel.com

drivers/gpu/drm/i915/i915_reg.h

@@ -8420,7 +8420,7 @@ enum skl_power_gate {
 #define  SKL_PW_TO_PG(pw)			((pw) - SKL_DISP_PW_1 + SKL_PG1)
 #define  SKL_FUSE_PG_DIST_STATUS(pg)		(1 << (27 - (pg)))
 
-#define _CNL_AUX_REG_IDX(pw)		((pw - 1) >> 4)
+#define _CNL_AUX_REG_IDX(pw)		((pw) - 9)
 #define _CNL_AUX_ANAOVRD1_B		0x162250
 #define _CNL_AUX_ANAOVRD1_C		0x162210
 #define _CNL_AUX_ANAOVRD1_D		0x1622D0