RDMA/amso1100: Add check if cache memory was allocated before freeing it
There is a path in handle_vq() where kmem_cache_free() can be called
with pointer to a local variable. It can happen if vq_repbuf_alloc()
failed to allocate memory from cache and req is NULL.
The patch adds check if cache memory was allocated before freeing it.
Found by Linux Driver Verification project (linuxtesting.org).