Userland: Use kmalloc_array() where appropriate

Userland/Libraries/LibC/dirent.cpp

@@ -255,7 +255,7 @@ int scandir(const char* dir_name,
     }
 
     const int size = tmp_names.size();
-    auto names = (struct dirent**)malloc(size * sizeof(struct dirent*));
+    auto** names = static_cast<struct dirent**>(kmalloc_array(size, sizeof(struct dirent*)));
     for (auto i = 0; i < size; i++) {
         names[i] = tmp_names[i];
     }

Userland/Libraries/LibC/stdlib.cpp

@@ -350,7 +350,7 @@ int putenv(char* new_var)
 
     // At this point, we need to append the new var.
     // 2 here: one for the new var, one for the sentinel value.
-    char** new_environ = (char**)malloc((environ_size + 2) * sizeof(char*));
+    auto** new_environ = static_cast<char**>(kmalloc_array(environ_size + 2, sizeof(char*)));
     if (new_environ == nullptr) {
         errno = ENOMEM;
         return -1;