fuse: use strscpy instead of strcpy

fuse: use strscpy instead of strcpy

As pointed out in [1], strcpy() is deprecated in favor of strscpy().

Furthermore, the size of the buffer for the name to be copied is well known
at this point since we are going to move the pointer by that much on the
next line.  Hence, it's safe to assume 'namelen' for the size of the string
to be copied.

[1] https://github.com/KSPP/linux/issues/88

Signed-off-by: Miquel Sabaté Solà <mssola@mssola.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>