RDMA/srpt: Use flex array destination for memcpy()

RDMA/srpt: Use flex array destination for memcpy()

In preparation for FORTIFY_SOURCE performing run-time destination buffer
bounds checking for memcpy(), specify the destination output buffer
explicitly, instead of asking memcpy() to write past the end of what looked
like a fixed-size object.

Notice that srp_rsp[] is a pointer to a structure that contains
flexible-array member data[]:

struct srp_rsp {
	...
	__be32	sense_data_len;
	__be32	resp_data_len;
	u8	data[];
};

link: https://github.com/KSPP/linux/issues/201
Signed-off-by: Hangyu Hua <hbh25y@gmail.com>
Link: https://lore.kernel.org/r/20220909022943.8896-1-hbh25y@gmail.com
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Leon Romanovsky <leon@kernel.org>