tiny-printf: Correct return values

The sprintf() etc. functions are supposed to return the length of the
string written, but do not. Fix this by checking the amount of buffer
space used.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/lib/tiny-printf.c b/lib/tiny-printf.c
index 9a70c60..64dee77 100644
--- a/lib/tiny-printf.c
+++ b/lib/tiny-printf.c
@@ -365,16 +365,15 @@
 {
 	struct printf_info info;
 	va_list va;
-	int ret;
 
 	va_start(va, fmt);
 	info.outstr = buf;
 	info.putc = putc_outstr;
-	ret = _vprintf(&info, fmt, va);
+	_vprintf(&info, fmt, va);
 	va_end(va);
 	*info.outstr = '\0';
 
-	return ret;
+	return info.outstr - buf;
 }
 
 #if CONFIG_IS_ENABLED(LOG)
@@ -382,14 +381,13 @@
 int vsnprintf(char *buf, size_t size, const char *fmt, va_list va)
 {
 	struct printf_info info;
-	int ret;
 
 	info.outstr = buf;
 	info.putc = putc_outstr;
-	ret = _vprintf(&info, fmt, va);
+	_vprintf(&info, fmt, va);
 	*info.outstr = '\0';
 
-	return ret;
+	return info.outstr - buf;
 }
 #endif
 
@@ -398,16 +396,15 @@
 {
 	struct printf_info info;
 	va_list va;
-	int ret;
 
 	va_start(va, fmt);
 	info.outstr = buf;
 	info.putc = putc_outstr;
-	ret = _vprintf(&info, fmt, va);
+	_vprintf(&info, fmt, va);
 	va_end(va);
 	*info.outstr = '\0';
 
-	return ret;
+	return info.outstr - buf;
 }
 
 void print_grouped_ull(unsigned long long int_val, int digits)