fs: Mark get_filesystem_list() as __init function.

"int get_filesystem_list(char * buf)" is called by only
"static void __init get_fs_names(char *page)".
We can mark get_filesystem_list() as "__init".

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>