ACPICA: Update dsmethod.c to get rid of unused variable warning

All the 3 major C compilers (MSVC, GCC, LLVM/Clang) warn about
the unused variable i after the removal of its usage by PR #1031
addressing Issue #1027

Link: https://github.com/acpica/acpica/commit/6d235320


Signed-off-by: Saket Dumbre <saket.dumbre@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>