Bug#886201: libffi: mips/ffi.c fix jr encoding for r6

[YunQiang Su]

Package: src:libffi
Version: 3.2.1-7

in mips/ffi.c, there are some binary encoding for some instructions,
while `jr' changes its encoding.

https://github.com/libffi/libffi/pull/401

-- 
YunQiang Su