staging: sm750: Fix lynxfb_ops_imageblit() if image->depth != 1

If image->depth != 1, lynxfb_ops_imageblit() should fallback to call
cfb_imageblit(), not return directly. Otherwise it can't display the
boot logo.

Cc: Teddy Wang <teddy.wang@siliconmotion.com>
Acked-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Signed-off-by: Huacai Chen <chenhc@lemote.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>