Fix build failure with macro MEM_DEBUG_MSG

[pcolberg]

Found this as part of debugging for implementing #103:

../../src/acl_kernel.cpp:2856:59: error: ‘needed_physical_id’ was not declared in this scope
         printf("needed_physical_id %d needed_mem_id %d ", needed_physical_id,
                                                           ^~~~~~~~~~~~~~~~~~

[pcolberg]

Klocwork is failing in a guarded section:

fpga-runtime-for-opencl/src/acl_mem.cpp

Lines 4478 to 4483 in 5f6af56

	#ifdef MEM_DEBUG_MSG
	printf("acl_reserve_buffer_block finished block_allocation:%zx, range:%zx - "
	"%zx \n",
	(size_t)block_allocation, (size_t)(block_allocation->range.begin),
	(size_t)(block_allocation->range.next));
	#endif

174 (Local) /__w/fpga-runtime-for-opencl/fpga-runtime-for-opencl/src/acl_mem.cpp:4479 UFM.DEREF.MIGHT (1:Critical) Analyze
Object 'block_allocation' was dereferenced at line 4479 after being freed by calling 'acl_delete<acl_block_allocation_t>' at line 4475
  * acl_mem.cpp:4450: block_allocation==nullptr is false
  * acl_mem.cpp:4456: mem->reserved_allocations[physical_device_id] .size() >target_mem_id is true
  * acl_mem.cpp:4457: mem->reserved_allocations[physical_device_id] [target_mem_id] ==0 is true
  * acl_mem.cpp:4458: mem->reserved_allocations_count[physical_device_id] [target_mem_id] ==0 is true
  * acl_mem.cpp:4470: result is false
  * acl_mem.cpp:4475: 'block_allocation' is freed by calling 'acl_delete<acl_block_allocation_t>'.
    * acl_support.h:31: Tracking 't'.
    * acl_support.h:31: 't' is freed by calling 'delete'.
  * acl_mem.cpp:4479: Freed pointer 'block_allocation' is used by calling 'printf'.

[zibaiwan]

Thanks for fixing this bug Peter!