Older platforms and Virtual platforms which doesn't have support for
bluetooth device in ACPI firmware will not have valid ACPI handle.
Check for validity of handle before accessing.

dmesg log from simics environment (virtual platform):

BUG: unable to handle kernel NULL pointer dereference at
0000000000000018
IP: acpi_ns_walk_namespace+0x5c/0x278
PGD 0 P4D 0
Oops: 0000 [#1] SMP PTI
Modules linked in: bnep intel_powerclamp coretemp kvm_intel
kvm irqbypass intel_cstate input_leds joydev serio_raw mac_hid
btusb(OE) btintel(OE) bluetooth(OE) lpc_ich compat(OE) ecdh_generic
i7core_edac i5500_temp shpchp binfmt_misc sch_fq_codel parport_pc ppdev
lp parport ip_tables x_tables autofs4 hid_generic usbhid hid e1000e
psmouse ahci pata_acpi libahci ptp pps_core floppy
CPU: 0 PID: 35 Comm: kworker/u3:0 Tainted: G           OE
4.15.0-140-generic #144-Ubuntu
Hardware name: Simics Simics, BIOS Simics 01/01/2011
Workqueue: hci0 hci_power_on [bluetooth]
RIP: 0010:acpi_ns_walk_namespace+0x5c/0x278
RSP: 0000:ffffaa9c0049bba8 EFLAGS: 00010246
RAX: 0000000000000001 RBX: 0000000000001001 RCX: 0000000000000010
RDX: ffffffff92ea7e27 RSI: ffffffff92ea7e10 RDI: 00000000000000c8
RBP: ffffaa9c0049bbf8 R08: 0000000000000000 R09: ffffffffc05b39d0
R10: 0000000000000000 R11: 0000000000000001 R12: 0000000000000001
R13: 0000000000000000 R14: ffffffffc05b39d0 R15: ffffaa9c0049bc70
FS:  0000000000000000(0000) GS:ffff8be73fc00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000018 CR3: 0000000075f0e000 CR4: 00000000000006f0

Fixes: 294d749b ("Bluetooth: btintel: Iterate only bluetooth device ACPI entries")
Signed-off-by: Kiran K <kiran.k@intel.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>