linux/export: Fix alignment for 64-bit ksymtab entries

An alignment of 4 bytes is wrong for 64-bit platforms which don't define
CONFIG_HAVE_ARCH_PREL32_RELOCATIONS (which then store 64-bit pointers).
Fix their alignment to 8 bytes.

Fixes: ddb5cdba

 ("kbuild: generate KSYMTAB entries by modpost")
Signed-off-by: Helge Deller <deller@gmx.de>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>