lib: export vsscanf

The function was missing from exports, even though it loooks like the
intent of the implementation in sscanf.c was to have it exported.

Signed-off-by: Samuel Dionne-Riel <samuel@dionne-riel.com>
Cc: Simon Glass <sjg@chromium.org>
Reviewed-by: Simon Glass <sjg@chromium.org>

include/vsprintf.h

@@ -307,6 +307,14 @@ char *strmhz(char *buf, unsigned long hz);
  */
 void str_to_upper(const char *in, char *out, size_t len);
 
+/**
+ * vsscanf - Unformat a buffer into a list of arguments
+ * @buf:	input buffer
+ * @fmt:	format of buffer
+ * @args:	arguments
+ */
+int vsscanf(const char *inp, char const *fmt0, va_list ap);
+
 /**
  * sscanf - Unformat a buffer into a list of arguments
  * @buf:	input buffer