Add missing init_list_head for the registered buffer list.
Absence of the init could lead to a unhandled kernel paging
request as below, when streamon/streamoff are called in row.

[338046.571321] Unable to handle kernel paging request at virtual address fffffffffffffe00
[338046.574849] pgd = ffff800034820000
[338046.582381] [fffffffffffffe00] *pgd=00000000b60f5003[338046.582545]
, *pud=00000000b1f31003
, *pmd=0000000000000000[338046.592082]
[338046.597754] Internal error: Oops: 96000004 [#1] PREEMPT SMP
[338046.601671] Modules linked in: venus_enc venus_dec venus_core
usb_f_ecm g_ether usb_f_rndis u_ether libcomposite ipt_MASQUERADE
nf_nat_masquerade_ipv4 arc4 wcn36xx mac80211 btqcomsmd btqca iptable_nat
nf_co]
[338046.662408] CPU: 0 PID: 5433 Comm: irq/160-venus Tainted: G        W
4.9.39+ #232
[338046.668024] Hardware name: Qualcomm Technologies, Inc. APQ 8016 SBC
(DT)
[338046.675268] task: ffff80003541cb00 task.stack: ffff800026e20000
[338046.682097] PC is at venus_helper_release_buf_ref+0x28/0x88
[venus_core]
[338046.688282] LR is at vdec_event_notify+0xe8/0x150 [venus_dec]
[338046.695029] pc : [<ffff000000af6c48>] lr : [<ffff000000a6fc60>]
pstate: a0000145
[338046.701256] sp : ffff800026e23bc0
[338046.708494] x29: ffff800026e23bc0 x28: 0000000000000000
[338046.718853] x27: ffff000000afd4f8 x26: ffff800031faa700
[338046.729253] x25: ffff000000afd790 x24: ffff800031faa618
[338046.739664] x23: ffff800003e18138 x22: ffff800002fc9810
[338046.750109] x21: ffff800026e23c28 x20: 0000000000000001
[338046.760592] x19: ffff80002a13b800 x18: 0000000000000010
[338046.771099] x17: 0000ffffa3d01600 x16: ffff000008100428
[338046.781654] x15: 0000000000000006 x14: ffff000089045ba7
[338046.792250] x13: ffff000009045bb6 x12: 00000000004f37c8
[338046.802894] x11: 0000000000267211 x10: 0000000000000000
[338046.813574] x9 : 0000000000032000 x8 : 00000000dc400000
[338046.824274] x7 : 0000000000000000 x6 : ffff800031faa728
[338046.835005] x5 : ffff80002a13b850 x4 : 0000000000000000
[338046.845793] x3 : fffffffffffffdf8 x2 : 0000000000000000
[338046.856602] x1 : 0000000000000003 x0 : ffff80002a13b800
Signed-off-by: Stanimir Varbanov <stanimir.varbanov@linaro.org>
Signed-off-by: Hans Verkuil <hansverk@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>