MIPS: OCTEON: Replace SIZEOF_FIELD() macro

Switch to the standard sizeof_field() macro to find the size of a member
of a struct and remove the custom SIZEOF_FIELD() macro.

Signed-off-by: Pankaj Bharadiya <pankaj.laxminarayan.bharadiya@intel.com>
Link: https://lore.kernel.org/r/20190924105839.110713-4-pankaj.laxminarayan.bharadiya@intel.com
Co-developed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Kees Cook <keescook@chromium.org>