firewire: nosy: fix list corruption by NOSY_IOC_STOP
firewire: nosy: fix list corruption by NOSY_IOC_STOP

nosy_stop_snoop() would blow up the second time it was called without
nosy_start_snoop() in between.

Signed-off-by: Stefan Richter <fbd796546fc801b34e01e453c6fd30283e012038@s5r6.in-berlin.de>

KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs