drm/i915/psr: Check for the specific AUX_FRAME_SYNC cap bit.

The cap check should be specifically for bit 0 instead of any bit.

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Fixes: 474d1ec4 ("drm/i915/skl: Enabling PSR2 SU with frame sync")
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180223221520.18464-4-dhinakaran.pandiyan@intel.com