x86/boot/compressed: Don't declare __force_order in kaslr_64.c

x86/boot/compressed: Don't declare __force_order in kaslr_64.c

GCC 10 changed the default to -fno-common, which leads to

    LD      arch/x86/boot/compressed/vmlinux
  ld: arch/x86/boot/compressed/pgtable_64.o:(.bss+0x0): multiple definition of `__force_order'; \
    arch/x86/boot/compressed/kaslr_64.o:(.bss+0x0): first defined here
  make[2]: *** [arch/x86/boot/compressed/Makefile:119: arch/x86/boot/compressed/vmlinux] Error 1

Since __force_order is already provided in pgtable_64.c, there is no
need to declare __force_order in kaslr_64.c.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20200124181811.4780-1-hjl.tools@gmail.com