safe_mmap(): Fix compiler warning in tst_res() format

The length variable has type size_t so the appropriate format is %zu.

Link: https://lore.kernel.org/ltp/20240507155225.14126-1-mdoucha@suse.cz/
Fixes: ff5f945 ("Print prot flag when SAFE_MMAP() fails")
Reviewed-by: Petr Vorel <pvorel@suse.cz>
Signed-off-by: Martin Doucha <mdoucha@suse.cz>

include/tst_safe_macros.h

@@ -281,7 +281,7 @@ static inline void *safe_mmap(const char *file, const int lineno,
 	tst_prot_to_str(prot, prot_buf);
 
 	tst_res_(file, lineno, TDEBUG,
-		"mmap(%p, %ld, %s(%x), %d, %d, %ld)",
+		"mmap(%p, %zu, %s(%x), %d, %d, %ld)",
 		addr, length, prot_buf, prot, flags, fd, offset);
 
 	rval = mmap(addr, length, prot, flags, fd, offset);