blktrace segfault

blktrace segfault

Core was generated by `blktrace -d /dev/hdc'.
Program terminated with signal 11, Segmentation fault.
#0  0xb7e4cdec in ?? ()
(gdb) where
#0  0xb7e4cdec in ?? ()
#1  0xb7dbf000 in ?? ()
#2  0x00021000 in ?? ()
#3  0xb7dee6e8 in ?? ()
#4  0x0804ecf0 in ?? ()
#5  0x00000001 in ?? ()
#6  0x6c616367 in ?? ()
#7  0xbfee3f68 in ?? ()
#8  0xb7f51300 in ?? ()
#9  0x00000168 in ?? ()
#10 0x0804ecf0 in ?? ()
#11 0x00000001 in ?? ()
#12 0xbfee3f88 in ?? ()
#13 0xbfee3f68 in ?? ()
#14 0x080499dc in close_thread (tip=0xb7f1eff4) at blktrace.c:637
Backtrace stopped: frame did not save the PC
(gdb)

the below diff fix the same.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>