monitor: Fix potential memory leak

monitor: Fix potential memory leak

If the mainloop_add_fd() returns with failure, the destroy callback is
never called so any reosurces need to be released never freed/closed.

This potential leakage is checked with valgrind after failing the
mainloop_add_fd() function manually.

   ==258684== 1,500 bytes in 1 blocks are definitely lost in loss record 3 of 3
   ==258684==    at 0x483BB1A: calloc (vg_replace_malloc.c:760)
   ==258684==    by 0x123F1A: open_channel (control.c:1058)
   ==258684==    by 0x125B09: control_tracing (control.c:1540)
   ==258684==    by 0x122764: main (main.c:255)
   ==258684==
   ==258684== LEAK SUMMARY:
   ==258684==    definitely lost: 1,500 bytes in 1 blocks
   ==258684==    indirectly lost: 0 bytes in 0 blocks
   ==258684==      possibly lost: 0 bytes in 0 blocks
   ==258684==    still reachable: 48 bytes in 2 blocks
   ==258684==         suppressed: 0 bytes in 0 blocks

This patch frees/closes the resources if the function returns with
failure.

Signed-off-by: Anuj Jain <anuj01.jain@samsung.com>
Signed-off-by: Ayush Garg <ayush.garg@samsung.com>