[BUG] video: fbdev: broadsheetfb: Possible null function pointers

[bai]

In Linux-4.16, drivers/video/fbdev/broadsheetfb.c,

158. static void broadsheet_mmio_send_cmdargs(...) {
             ......
163.     par->board->mmio_write(...);
             ......
166.     par->board->mmio_write(...);
167. }

For x86 kernel configuration, I find that there is no assignment of the 
function pointer ".mmio_write" in the kernel code.
So calling the function pointer in lines 163 and 166 may cause a null 
pointer dereference.

In this file, there are many calls to this function pointer...


Best wishes,
Jia-Ju Bai