drivers: rmnet_shs: Force flushing in fb timer

Add force flush in fb timer to force flush gold to silver
transfers.

Change-Id: I1503f85c4a0502b98a6ccb31a5b4ac6599ed190a
Acked-by: Raul Martinez <mraul@qti.qualcomm.com>
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>