Avoid a VLA by using a real constant expression instead of a variable.
The compiler should be able to optimize the original code and avoid
using an actual VLA.  Anyway this change is useful because it will avoid
a false positive with -Wvla, it might also help the compiler generating
better code.

Link: http://lkml.kernel.org/r/1520970710-19732-1-git-send-email-s.mesoraca16@gmail.comSigned-off-by: Salvatore Mesoraca <s.mesoraca16@gmail.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Joseph Qi <jiangqi903@gmail.com>
Cc: Changwei Ge <ge.changwei@h3c.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>