callback functions (get_sink_info_change_cb, get_source_info_change_cb) causes sig 11 crash in mixer

steps to reproduce:

      1) from GUI, start MIXER

      2) Go to SETTINGS/BLUETOOTH

      3) connect some listed device

m3ulcb login: [   99.135391] input: 9C:5C:F9:88:7F:D2 as /devices/virtual/input/input2
[  130.456695] input: 9C:5C:F9:88:7F:D2 as /devices/virtual/input/input3
[  133.375134] PaClient mainlo[3509]: unhandled level 2 translation fault (11) at 0x00000004, esr 0x92000006
[  133.385607] pgd = ffff8005e5917000
[  133.389345] [00000004] *pgd=000000062591a003[  133.394169] , *pud=000000062591b003
, *pmd=0000000000000000[  133.399821]
[  133.401504]
[  133.403094] CPU: 0 PID: 3509 Comm: PaClient mainlo Tainted: G           O    4.9.0-yocto-standard #2
[  133.412418] Hardware name: Renesas M3ULCB board based on r8a7796 (DT)
[  133.418980] task: ffff8005e5892400 task.stack: ffff8005e5944000
[  133.424980] PC is at 0x40c2bc
[  133.427941] LR is at 0x40c218
[  133.430967] pc : [<000000000040c2bc>] lr : [<000000000040c218>] pstate: 60000000
[  133.438412] sp : 0000ffff63ffe120
[  133.441771] x29: 0000ffff63ffe120 x28: 0000000000000004
[  133.447128] x27: 0000000000421000 x26: 000000000040cc28
[  133.452533] x25: 0000ffff63ffe18c x24: 0000ffff63ffe190
[  133.457957] x23: 0000000023f190f0 x22: 0000ffff63ffe248
[  133.463327] x21: 0000ffff63ffe2f8 x20: 0000ffff5c00e080
[  133.468718] x19: 0000000000000000 x18: 0000000000000000
[  133.474088] x17: 0000ffff7acf1010 x16: 0000ffff7ad1e780
[  133.479458] x15: 000037ce9ea11b66 x14: 0000000000000014
[  133.484828] x13: 0068746f6f746575 x12: 6c622d647261632d
[  133.490881] x11: 43395f7665642f30 x10: 6963682f7a65756c
[  133.496321] x9 : 0000ffff5c002740 x8 : 0000ffff63ffe190
[  133.501740] x7 : 0000000000000441 x6 : 000000000000004e
[  133.507195] x5 : 0000ffff5c00e080 x4 : 0000ffff5c00e0c0
[  133.512584] x3 : 0000ffff5c00e080 x2 : 0000000017b967f8
[  133.517977] x1 : 0000ffff63ffe18c x0 : 0000ffff5c00e080
[  133.523352]
[  133.524943] audit: type=1701 audit(1512054665.723:9): auid=4294967295 uid=0 gid=0 ses=4294967295 subj=User::App::mixer pid=3493 comm=5061436C69656E74206D61696E6C6F exe="/var/local/lib/afm/applications/mixer/0.1/bin/mixer" sig=11