perf jevents: Fix leak of mapfile memory

The memory for global pointer is never freed during normal program
execution, so let's do that in the main function exit as a good
programming practice.

A stray blank line is also removed.

Reported-by: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: John Garry <john.garry@huawei.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: James Clark <james.clark@arm.com>
Cc: Joakim Zhang <qiangqing.zhang@nxp.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will@kernel.org>
Cc: linuxarm@huawei.com
Link: http://lore.kernel.org/lkml/1583406486-154841-2-git-send-email-john.garry@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>