ufs: don't truncate longer ufs2 fast symlinks

ufs2 fast symlinks can be twice as long as ufs ones, however the code
was using the ufs size in various places. Fix that so ufs2 symlinks over
60 characters aren't truncated.

Note that we copy the entire area instead of using the maxsymlinklen field
from the superblock. This way we will be more robust against corruption (of
the superblock).

While we are at it, use memcpy instead of open-coding it with for loops.

Signed-off-by: Duane Griffin <duaneg@dghda.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>