sections.h: simplify LINUX_SECTION_ALIGNMENT()

This does not need to use __typeof__(), since we have
the name just refer to it directly. There are quite
a few users of this style in the kernel already as well,
example, one example: net/netfilter/xt_repldata.h

It doesn't seem worth generalizing this into
include/linux/compiler-gcc.h as we're providing all our
attributes in one shot.

Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>