ACPICA: Tables: Fix multiple ACPI_FREE()s around acpi_tb_add_table().

Currently there are following issues in acpi_tb_add_table():
Following logic is currently correct:
1. When a table is allocated in acpi_ex_load_op(), if a reloading happens,
   the allocated memory is freed by acpi_tb_add_table() and AE_OK is
   returned to the caller to avoid the caller to free it again.
Following logic is currently incorrect:
1. When a table is allocated in acpi_ex_load_op() or by the
   acpi_load_table() caller, if the table is already loaded, there will be
   twice ACPI_FREE() called for the same pointer when acpi_tb_add_table()
   returns AE_ALREADY_EXISTS.

This patch only fixes the above incorrect logic in acpi_tb_add_table():
1. Only invoke acpi_tb_delete_table() if AE_OK is going to be returned.
2. After doing so, we do not invoke ACPI_FREE() when returning AE_OK;

Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Bob Moore <robert.moore@intel.com>
[rjw: Subject]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>