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

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