_MAT can inadvertently return an Integer instead of a Buffer
if the return value has been read from a Field whose width is
less than or equal to the global integer width (32 or 64 bits).
ACPICA BZ 810.

http://www.acpica.org/bugzilla/show_bug.cgi?id=810Signed-off-by: Lin Ming <ming.m.lin@intel.com>
Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>