drm/vkms: Use drm_crtc_vblank_crtc()

drm/vkms: Use drm_crtc_vblank_crtc()

Replace the open coded drm_crtc_vblank_crtc() with the real
thing.

Cc: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Cc: Melissa Wen <melissa.srw@gmail.com>
Cc: "Maíra Canal" <mairacanal@riseup.net>
Cc: Haneen Mohammed <hamohammed.sa@gmail.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240408190611.24914-5-ville.syrjala@linux.intel.com
Reviewed-by: Maíra Canal <mcanal@igalia.com>