The offset of block allocator, ba->offset, should not be changed during
fixed address allocating, for the caller may treat it as the offset of
allocated memory and use it. In the case that we allocate more than 1
blocks, we should make sure this offset is correct.

Here introduces a temp allocator for the later continuous allocating.
Signed-off-by: NJie Yang <yang.jie@intel.com>
Signed-off-by: NMark Brown <broonie@kernel.org>