accel/amdxdna: Fix cu_idx being cleared by memset() during command setup

accel/amdxdna: Fix cu_idx being cleared by memset() during command setup

For one command type, cu_idx is assigned before calling memset() on the
command structure. This results in cu_idx being overwritten, causing the
firmware to receive an incomplete or invalid command and leading to
unexpected command failures.

Fix this by moving the memset() call before initializing cu_idx so that
all fields are populated in the correct order.

Fixes: 71829d7f2f70 ("accel/amdxdna: Use MSG_OP_CHAIN_EXEC_NPU when supported")
Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>
Signed-off-by: Lizhi Hou <lizhi.hou@amd.com>
Link: https://patch.msgid.link/20251209211639.1636888-1-lizhi.hou@amd.com