tools: sunxi: avoid read after end of string

tools: sunxi: avoid read after end of string

The evaluation of option -c is incorrect:

According to the C99 standard endptr in the first strtol is always
set as &endptr is not NULL.
So the first part of the or condition is always true.
If all digits in optarg are valid endptr will point to the closing \0
and the second strtol will read beyond the end of the string optarg
points to.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Acked-by: Boris Brezillon <boris.brezillon@free-electrons.com>