Update tee_ta_manager.c

Fix user heap corruption by usr_params

Avoids corruption of heap by usr_params, and vice versa, when 
stack_size+heap_size is a multiple of 1 MiB. usr_params was
previously unintentionally stored just outside the allocated
stack. If there is not enough padding between stack and heap,
usr_params will overwrite a part of the heap.
This can't work. The only time nbr_sections is too large is when p->memref.size is a multiple of SECTION_SIZE (1 MiB).

nbr_sections is the number of section that this parameter need to have mapped while py_offset is the physical address  shifted to count MiBs instead of bytes.