drm/i915/display: Fix TRANS_DDI_MST_TRANSPORT_SELECT definition

TRANS_DDI_MST_TRANSPORT_SELECT is 2 bits wide not 3, it was taking
one bit from EDP/DSI Input Select.

Fixes: b3545e08 ("drm/i915/tgl: add support to one DP-MST stream")
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191107214559.77087-1-jose.souza@intel.com

drivers/gpu/drm/i915/i915_reg.h

@@ -9675,7 +9675,7 @@ enum skl_power_gate {
 #define  TRANS_DDI_EDP_INPUT_A_ONOFF	(4 << 12)
 #define  TRANS_DDI_EDP_INPUT_B_ONOFF	(5 << 12)
 #define  TRANS_DDI_EDP_INPUT_C_ONOFF	(6 << 12)
-#define  TRANS_DDI_MST_TRANSPORT_SELECT_MASK	REG_GENMASK(12, 10)
+#define  TRANS_DDI_MST_TRANSPORT_SELECT_MASK	REG_GENMASK(11, 10)
 #define  TRANS_DDI_MST_TRANSPORT_SELECT(trans)	\
 	REG_FIELD_PREP(TRANS_DDI_MST_TRANSPORT_SELECT_MASK, trans)
 #define  TRANS_DDI_HDCP_SIGNALLING	(1 << 9)