Fix clang warning

Fix clang warning

Clang issues a warning about what we are really intending to do. Use an
explicit type as argument to sizeof().

tracer.c:1152:28: warning: 'memcpy' call operates on objects of type 'const char' while the size is based on a different type 'const char *' [-Wsizeof-pointer-memaccess]
                memcpy(&ptr, ptr, sizeof(ptr));
                             ~~~         ^~~
tracer.c:1152:28: note: did you mean to provide an explicit length?
                memcpy(&ptr, ptr, sizeof(ptr));
                                         ^~~
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>