kbuild: Fix bug in crc symbol generating of kernel and modules

The scripts/genksyms/genksyms.c uses hardcoded "__crc_" prefix for
crc symbols in kernel and modules. The prefix should be replaced by
"MODULE_SYMBOL_PREFIX##__crc_" otherwise there will be warnings when
MODULE_SYMBOL_PREFIX is not NULL.

I am sorry my last patch for this issue is actually wrong. I revert
it in this patch.

Signed-off-by: Luke Yang <luke.adi@gmail.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>