perf jit: memset() variable 'st' using the correct size

perf jit: memset() variable 'st' using the correct size

The current code is memsetting the 'struct stat' variable 'st' with the size of
'stat' (which turns out to be 1 byte) rather than the size of variable 'sz'.

Committer notes:

sizeof(function) isn't valid, the result depends on the compiler used, with
gcc, enabling pedantic warnings we get:

  $ cat sizeof_function.c
  #include <sys/types.h>
  #include <sys/stat.h>
  #include <unistd.h>
  #include <stdio.h>

  int main(void)
  {
	  printf("sizeof(stat)=%zd, stat=%p\n", sizeof(stat), stat);
	  return 0;
  }
  $ readelf -sW sizeof_function | grep -w stat
      49: 0000000000400630    16 FUNC    WEAK   HIDDEN    13 stat
  $ cc -pedantic sizeof_function.c   -o sizeof_function
  sizeof_function.c: In function ‘main’:
  sizeof_function.c:8:46: warning: invalid application of ‘sizeof’ to a function type [-Wpointer-arith]
    printf("sizeof(stat)=%zd, stat=%p\n", sizeof(stat), stat);
                                              ^
  $ ./sizeof_function
  sizeof(stat)=1, stat=0x400630
  $

  Standard C, section 6.5.3.4:

  "The sizeof operator shall not be applied to an expression that has function
   type or an incomplete type, to the parenthesized name of such a type,
   or to an expression that designates a bit-field member."

  http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Fixes: 9b07e27f88b9 ("perf inject: Add jitdump mmap injection support")
Link: http://lkml.kernel.org/r/1461020838-9260-1-git-send-email-colin.king@canonical.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>