'csum_partial' and 'csum_partial_copy_from_user' have already been
exported in "lib/", so need not export them again, or it will cause
compiling error.

The related error (with allmodconfig under unicore32):

    LD      vmlinux.o
  lib/built-in.o:(___ksymtab+csum_partial+0x0): multiple definition of `__ksymtab_csum_partial'
  arch/unicore32/kernel/built-in.o:(___ksymtab+csum_partial+0x0): first defined here
  lib/built-in.o:(___ksymtab+csum_partial_copy_from_user+0x0): multiple definition of `__ksymtab_csum_partial_copy_from_user'
  arch/unicore32/kernel/built-in.o:(___ksymtab+csum_partial_copy_from_user+0x0): first defined here
  make: *** [vmlinux] Error 1

Signed-off-by: Chen Gang <gang.chen.5i5j@gmail.com>
Acked-by: Xuetao Guan <gxt@mprc.pku.edu.cn>
Signed-off-by: Xuetao Guan <gxt@mprc.pku.edu.cn>