tracing: Fix memory leak in __create_synth_event()

tracing: Fix memory leak in __create_synth_event()

kmemleak report:
unreferenced object 0xc5a6f708 (size 8):
  comm "ftracetest", pid 1209, jiffies 4294911500 (age 6.816s)
  hex dump (first 8 bytes):
    00 c1 3d 60 14 83 1f 8a                          ..=`....
  backtrace:
    [<f0aa4ac4>] __kmalloc_track_caller+0x2a6/0x460
    [<7d3d60a6>] kstrndup+0x37/0x70
    [<45a0e739>] argv_split+0x1c/0x120
    [<c17982f8>] __create_synth_event+0x192/0xb00
    [<0708b8a3>] create_synth_event+0xbb/0x150
    [<3d1941e1>] create_dyn_event+0x5c/0xb0
    [<5cf8b9e3>] trace_parse_run_command+0xa7/0x140
    [<04deb2ef>] dyn_event_write+0x10/0x20
    [<8779ac95>] vfs_write+0xa9/0x3c0
    [<ed93722a>] ksys_write+0x89/0xc0
    [<b9ca0507>] __ia32_sys_write+0x15/0x20
    [<7ce02d85>] __do_fast_syscall_32+0x45/0x80
    [<cb0ecb35>] do_fast_syscall_32+0x29/0x60
    [<2467454a>] do_SYSENTER_32+0x15/0x20
    [<9beaa61d>] entry_SYSENTER_32+0xa9/0xfc
unreferenced object 0xc5a6f078 (size 8):
  comm "ftracetest", pid 1209, jiffies 4294911500 (age 6.816s)
  hex dump (first 8 bytes):
    08 f7 a6 c5 00 00 00 00                          ........
  backtrace:
    [<bbac096a>] __kmalloc+0x2b6/0x470
    [<aa2624b4>] argv_split+0x82/0x120
    [<c17982f8>] __create_synth_event+0x192/0xb00
    [<0708b8a3>] create_synth_event+0xbb/0x150
    [<3d1941e1>] create_dyn_event+0x5c/0xb0
    [<5cf8b9e3>] trace_parse_run_command+0xa7/0x140
    [<04deb2ef>] dyn_event_write+0x10/0x20
    [<8779ac95>] vfs_write+0xa9/0x3c0
    [<ed93722a>] ksys_write+0x89/0xc0
    [<b9ca0507>] __ia32_sys_write+0x15/0x20
    [<7ce02d85>] __do_fast_syscall_32+0x45/0x80
    [<cb0ecb35>] do_fast_syscall_32+0x29/0x60
    [<2467454a>] do_SYSENTER_32+0x15/0x20
    [<9beaa61d>] entry_SYSENTER_32+0xa9/0xfc

In __create_synth_event(), while iterating field/type arguments, the
argv_split() will return array of atleast 2 elements even when zero
arguments(argc=0) are passed. for e.g. when there is double delimiter
or string ends with delimiter

To fix call argv_free() even when argc=0.

Link: https://lkml.kernel.org/r/20210304094521.GA1826@cosmos
Signed-off-by: Vamshi K Sthambamkadi <vamshi.k.sthambamkadi@gmail.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>