usb: dwc3-msm: Set IOC bit in StartXFERCommand for DBM endpoints

If an endpoint is used in DBM mode then software should set IOC
bit in Start Transfer Command. Setting this bit causes DWC3 core
to fire interrupt on command completion. Since, DBM expects this
interrupt to be fired, hence, enable this. Otherwise DBM fails
later to intercept TRB read request from core.
Also, fix BUG in programming DBM's event buffer register.

Change-Id: I68ea5847a51f8fa05189de4836b6140932f80a26
Signed-off-by: Manu Gautam <mgautam@codeaurora.org>