drm/i915/cnl: Fix the CURSOR_COEFF_MASK used in DDI Vswing Programming

The Cursor Coeff is lower 6 bits in the PORT_TX_DW4 register
and hence the CURSOR_COEFF_MASK should be (0x3F << 0)

Fixes: 04416108ccea ("drm/i915/cnl: Add registers related to voltage
swing sequences.")
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1498785241-21138-1-git-send-email-manasi.d.navare@intel.com

drivers/gpu/drm/i915/i915_reg.h

@@ -1802,7 +1802,7 @@ enum skl_disp_power_wells {
 #define   POST_CURSOR_2(x)		((x) << 6)
 #define   POST_CURSOR_2_MASK		(0x3F << 6)
 #define   CURSOR_COEFF(x)		((x) << 0)
-#define   CURSOR_COEFF_MASK		(0x3F << 6)
+#define   CURSOR_COEFF_MASK		(0x3F << 0)
 
 #define _CNL_PORT_TX_DW5_GRP_AE		0x162354
 #define _CNL_PORT_TX_DW5_GRP_B		0x1623D4