The value of struct flash_driver::command can be NULL when the
flash driver does not need to add any new command.
Remove empty command definitions.
Change-Id: I5413967d4069030234469822d24e9825425ae012
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/7120
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>
Tested-by: jenkins