lib: os: cbprintf: Add assert to Z_CBPRINTF_ON_STACK_ALLOC

Add protection if number of string arguments exceed the limit
which currently is set to 32.

Signed-off-by: Krzysztof Chruscinski <krzysztof.chruscinski@nordicsemi.no>

include/sys/cbprintf_internal.h

@@ -359,6 +359,7 @@ union z_cbprintf_hdr {
  * multiple times. VLA is not always available.
  */
 #define Z_CBPRINTF_ON_STACK_ALLOC(_name, _len) \
+	__ASSERT(_len <= 32, "Too many string arguments."); \
 	uint8_t _name##_buf4[4]; \
 	uint8_t _name##_buf8[8]; \
 	uint8_t _name##_buf12[12]; \