parisc: sys_hpux: NUL terminator is one past the end

We allocate "len" number of chars so we should put the NUL at "len - 1"
to avoid corrupting memory.  Btw, strlen_user() is different from the
normal strlen() function because it includes NUL terminator in the
count.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Helge Deller <deller@gmx.de>