accel/ethosu: fix wrong weight index in NPU_SET_SCALE1_LENGTH on U85

accel/ethosu: fix wrong weight index in NPU_SET_SCALE1_LENGTH on U85

On non-U65 hardware (e.g. U85), opcode 0x4093 is NPU_SET_WEIGHT2_LENGTH.
The BASE handler for the same opcode correctly assigns to
st.weight[2].base, but the LENGTH handler mistakenly assigns cmds[1]
to st.weight[1].length instead of st.weight[2].length.

This leaves weight[2].length at its initialised sentinel value of
0xffffffff and corrupts weight[1].length with the user-supplied value,
breaking the software bounds-check state for both weight buffers on U85.

Fix the index to match the BASE handler.

Fixes: 5a5e9c0228e6 ("accel: Add Arm Ethos-U NPU driver")
Cc: stable@vger.kernel.org
Signed-off-by: Muhammad Bilal <meatuni001@gmail.com>
Link: https://patch.msgid.link/20260523210840.92039-3-meatuni001@gmail.com
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>