[PATCH 1/3][V2] lib: fix match_string() helper on -1 array size

[Alexandru Ardelean]

The documentation the `_match_string()` helper mentions that `n`
should be:
 * @n: number of strings in the array or -1 for NULL terminated arrays

The behavior of the function is different, in the sense that it exits on
the first NULL element in the array, regardless of whether `n` is -1 or a
positive number.

This patch changes the behavior, to exit the loop when a NULL element is
found and n == -1. Essentially, this aligns the behavior with the
doc-string.

There are currently many users of `match_string()`, and so, in order to go
through them, the next patches in the series will focus on doing some
cosmetic changes, which are aimed at grouping the users of
`match_string()`.

Signed-off-by: Alexandru Ardelean <alexandru.ardelean at analog.com>
---

Changelog v1 -> v2:
* split the initial series into just 3 patches that fix the
  `match_string()` helper and start introducing a new version of this
  helper, which computes array-size of static arrays

 lib/string.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/lib/string.c b/lib/string.c
index 6016eb3ac73d..e2cf5acc83bd 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -681,8 +681,11 @@ int match_string(const char * const *array, size_t n, const char *string)
 
 	for (index = 0; index < n; index++) {
 		item = array[index];
-		if (!item)
+		if (!item) {
+			if (n != (size_t)-1)
+				continue;
 			break;
+		}
 		if (!strcmp(item, string))
 			return index;
 	}
-- 
2.20.1