shdma: fixup sh_dmae_get_partial() calculation error

sh_desc->hw.tcr is controlling real data size,
and, register TCR is controlling data transfer count
which was xmit_shifted value of hw.tcr.
Current sh_dmae_get_partial() is calculating in different unit.
This patch fixes it.

This bug has been present since c014906a
("dmaengine: shdma: extend .device_terminate_all() to record partial
transfer"), which was added in 2.6.34-rc1.

Cc: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Acked-by: Guennadi Liakhovetski <g.liakhovetski+renesas@gmail.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>