sys: cbprintf: Fix performance-no-int-to-ptr warning

clang-tidy reports a performance-no-int-to-ptr warning due to the cast
(const char *)(uintptr_t)(v).

Previously, only char * was cast to const char *, but there's no downside
to constifying all pointer types.

This change updates the Z_CONSTIFY macro to apply const consistently,
which even aligns better with its name and resolves the warning.

Signed-off-by: Tim Pambor <tim.pambor@codewrights.de>

Author: tpambor

include/zephyr/sys/cbprintf_internal.h

@@ -560,7 +560,11 @@ extern "C" {
 #ifdef __cplusplus
 #define Z_CBPRINTF_ARG_SIZE(v) z_cbprintf_cxx_arg_size(v)
 #else
-#define Z_CONSTIFY(v) (_Generic((v), char * : (const char *)(uintptr_t)(v), default : (v)))
+#define Z_CONSTIFY(v) ({ \
+	__auto_type _uv = (v); \
+	__typeof__(_uv) const _cv = _uv; \
+	_cv; \
+})
 #define Z_CBPRINTF_ARG_SIZE(v) ({\
 	__auto_type __v = Z_ARGIFY(Z_CONSTIFY(v)); \
 	/* Static code analysis may complain about unused variable. */ \