Bluetooth: btintel_pcie: fix off-by-one bounds check in RX submit

btintel_pcie_submit_rx() used frbd_index > rxq->count to guard the
FRBD array access, allowing frbd_index == rxq->count to pass through
and index one element past the end of the array. Change the check to
>= rxq->count so every out-of-range index is rejected.

This issue was reported by Claude Mythos.

Fixes: c2b636b3f788 (Bluetooth: btintel_pcie: Add support for PCIe transport)
Signed-off-by: Sai Teja Aluvala <aluvala.sai.teja@intel.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>