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

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