binfmt_flat: fix arch/m32r and arch/microblaze flat_put_addr_at_rp()

Change the m32r flat_put_addr_at_rp() function to return int and
always return 0.

The microblaze function already returned 0 so just change its
function return type from void to int.

Seven (7) other arch-es already have this function as returning
an int type result.

Fixes: 468138d7 (binfmt_flat: flat_{get,put}_addr_from_rp()
	should be able to fail)

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>