mailbox: zynqmp-ipi: Fix out-of-bounds access in mailbox cleanup loop

mailbox: zynqmp-ipi: Fix out-of-bounds access in mailbox cleanup loop

The cleanup loop was starting at the wrong array index, causing
out-of-bounds access.
Start the loop at the correct index for zero-indexed arrays to prevent
accessing memory beyond the allocated array bounds.

Fixes: 4981b82ba2ff ("mailbox: ZynqMP IPI mailbox controller")
Signed-off-by: Harini T <harini.t@amd.com>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Jassi Brar <jassisinghbrar@gmail.com>