buildroot

support/mkusers: rename variable to avoid name clashing

The LINES variable is automatically set by bash to represent the number
of lines in the terminal. That variable can be set when the shell
receives SIGWINCH.

If the shell does receive SIGWINCH after our LINES array is filled, the
content of the array is mangled.

Rename the variable to avoid that.

Fixes #9456

Reported-by: George Y. <georgebrmz@oss3d.com>
Reported-by: Paul Stewart <paulstewartis@gmail.com>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Arnout Vandecappelle <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
(cherry picked from commit 00d34e8a6f378653a384c66d68f9a65e13b8034f)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>