What is the issue here: 
==36527== Invalid write of size 4
==36527==    at 0x1092C9: split_array (split_array.c:25)
==36527==    by 0x1093BC: main (split_array.c:59)
==36527==  Address 0x4a73144 is 4 bytes inside a block of size 6 alloc'd
==36527==    at 0x483B7F3: malloc (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==36527==    by 0x109245: split_array (split_array.c:19)
==36527==    by 0x1093BC: main (split_array.c:59)
==36527== 