tracing: Fix memory leak in test_gen_synth_cmd() and test_empty_synth_event()

In the Linux kernel, the following vulnerability has been resolved:

tracing: Fix memory leak in test_gen_synth_cmd() and test_empty_synth_event()

test_gen_synth_cmd() only free buf in fail path, hence buf will leak
when there is no failure. Add kfree(buf) to prevent the memleak. The
same reason and solution in test_empty_synth_event().

unreferenced object 0xffff8881127de000 (size 2048):
comm "modprobe", pid 247, jiffies 4294972316 (age 78.756s)
hex dump (first 32 bytes):
20 67 65 6e 5f 73 79 6e 74 68 5f 74 65 73 74 20 gen_synth_test
20 70 69 64 5f 74 20 6e 65 78 74 5f 70 69 64 5f pid_t next_pid_
backtrace:
[<000000004254801a>] kmalloc_trace+0x26/0x100
[<0000000039eb1cf5>] 0xffffffffa00083cd
[<000000000e8c3bc8>] 0xffffffffa00086ba
[<00000000c293d1ea>] do_one_initcall+0xdb/0x480
[<00000000aa189e6d>] do_init_module+0x1cf/0x680
[<00000000d513222b>] load_module+0x6a50/0x70a0
[<000000001fd4d529>] __do_sys_finit_module+0x12f/0x1c0
[<00000000b36c4c0f>] do_syscall_64+0x3f/0x90
[<00000000bbf20cf3>] entry_SYSCALL_64_after_hwframe+0x63/0xcd
unreferenced object 0xffff8881127df000 (size 2048):
comm "modprobe", pid 247, jiffies 4294972324 (age 78.728s)
hex dump (first 32 bytes):
20 65 6d 70 74 79 5f 73 79 6e 74 68 5f 74 65 73 empty_synth_tes
74 20 20 70 69 64 5f 74 20 6e 65 78 74 5f 70 69 t pid_t next_pi
backtrace:
[<000000004254801a>] kmalloc_trace+0x26/0x100
[<00000000d4db9a3d>] 0xffffffffa0008071
[<00000000c31354a5>] 0xffffffffa00086ce
[<00000000c293d1ea>] do_one_initcall+0xdb/0x480
[<00000000aa189e6d>] do_init_module+0x1cf/0x680
[<00000000d513222b>] load_module+0x6a50/0x70a0
[<000000001fd4d529>] __do_sys_finit_module+0x12f/0x1c0
[<00000000b36c4c0f>] do_syscall_64+0x3f/0x90
[<00000000bbf20cf3>] entry_SYSCALL_64_after_hwframe+0x63/0xcd