include/linux/hugetlb*.h: clean up code

Macro HUGETLBFS_SB is clear enough, so one statement is clearer than 3
lines statements.

Remove redundant return statements for non-return functions, which can
save lines, at least.

Signed-off-by: Chen Gang <gang.chen.5i5j@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>