[Crash-utility] fix bug of struct command

Hello Dave, The attachment is used to fix a bug of struct command. When using command like below, struct command displays wrong data. <cut> crash> task_struct.fs ffff88003dfb5540 fs = 140234226652928 crash> task_struct ffff88003dfb5540 ... es = 0, ds = 0, fsindex = 0, gsindex = 0, *fs = 140234226652928,* gs = 0, debugreg0 = 0, ... io_bitmap_ptr = 0x0, iopl = 0, io_bitmap_max = 0 }, *fs = 0xffff880037795f00,* files = 0xffff8800371b6940, ... <cut> fs showed by struct command is a member of "struct thread_struct thread;", not struct task_struct. This bug is involved by adding support to anonymous member modified by me... -- -- Regards Qiao Nuohan