RDMA/erdma: Remove unnecessary __GFP_ZERO flag

The dma_alloc_coherent() interface automatically zero the memory returned.
Thus, we do not need to specify the __GFP_ZERO flag explicitly when we call
dma_alloc_coherent().

Reviewed-by: Cheng Xu <chengyou@linux.alibaba.com>
Signed-off-by: Boshi Yu <boshiyu@linux.alibaba.com>
Link: https://lore.kernel.org/r/20240311113821.22482-4-boshiyu@alibaba-inc.com
Signed-off-by: Leon Romanovsky <leon@kernel.org>