lib/cmdline: fix get_option() for strings starting with hyphen

mainline inclusion
from mainline-v5.11-rc1
commit e291851d
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I7R8MK
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=e291851d65495739e4eede33b6bc387bb546a19b

--------------------------------

When string doesn't have an integer and starts from hyphen get_option()
may return interesting results.  Fix it to return 0.

The simple_strtoull() is used due to absence of simple_strtoul() in a boot
code on some architectures.

Note, the Fixes tag below is rather for anthropological curiosity.

Link: https://lkml.kernel.org/r/20201112180732.75589-4-andriy.shevchenko@linux.intel.com


Fixes: f68565831e72 ("Import 2.4.0-test2pre3")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Brendan Higgins <brendanhiggins@google.com>
Cc: David Gow <davidgow@google.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Cc: Vitor Massaru Iha <vitor@massaru.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Guo Mengqi <guomengqi3@huawei.com>