Bluetooth: btintel_pcie: Fix driver not posting maximum rx buffers

The driver was posting only 6 rx buffers, despite the maximum rx buffers
being defined as 16. Having fewer RX buffers caused firmware exceptions
in HID use cases when events arrived in bursts.

Exception seen on android 6.12 kernel.

E Bluetooth: hci0: Received hw exception interrupt
E Bluetooth: hci0: Received gp1 mailbox interrupt
D Bluetooth: hci0: 00000000: ff 3e 87 80 03 01 01 01 03 01 0c 0d 02 1c 10 0e
D Bluetooth: hci0: 00000010: 01 00 05 14 66 b0 28 b0 c0 b0 28 b0 ac af 28 b0
D Bluetooth: hci0: 00000020: 14 f1 28 b0 00 00 00 00 fa 04 00 00 00 00 40 10
D Bluetooth: hci0: 00000030: 08 00 00 00 7a 7a 7a 7a 47 00 fb a0 10 00 00 00
D Bluetooth: hci0: 00000000: 10 01 0a
E Bluetooth: hci0: ---- Dump of debug registers —
E Bluetooth: hci0: boot stage: 0xe0fb0047
E Bluetooth: hci0: ipc status: 0x00000004
E Bluetooth: hci0: ipc control: 0x00000000
E Bluetooth: hci0: ipc sleep control: 0x00000000
E Bluetooth: hci0: mbox_1: 0x00badbad
E Bluetooth: hci0: mbox_2: 0x0000101c
E Bluetooth: hci0: mbox_3: 0x00000008
E Bluetooth: hci0: mbox_4: 0x7a7a7a7a

Signed-off-by: Chandrashekar Devegowda <chandrashekar.devegowda@intel.com>
Signed-off-by: Kiran K <kiran.k@intel.com>
Fixes: c2b636b3 ("Bluetooth: btintel_pcie: Add support for PCIe transport")
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>