soc: swr-mstr-ctrl: update sampleinterval low only when disconnect swr port

Register SWRM_DP_PORT_CTRL_BANK only has sample interval low.
When disconnecting swr port, only update sampleinterval low for
active port.

Change-Id: Iec7c266fce76ce140a43f9e410126ad5560f5b81
Signed-off-by: Meng Wang <mengw@codeaurora.org>