usb: u_bam_data.c: Use already initialized BAM connection indexes

Driver already initializes src/dst_connection_idx on connect for
BAM2BAM transports, but, it still queries the same again. Fix this
by using existing src/dst_connect_idx.

Change-Id: Ia500876e491071e00a08adcc36f2a8ab7e0fc1ff
Signed-off-by: Manu Gautam <mgautam@codeaurora.org>