mhi: core: Fix out of bound channel id handling

If transfer completion event ring element includes invalid
channel id, driver continues in a while loop without
incrementing local event ring read pointer. This results
into infinite loop. Hence recycle the current element and
move to next event ring element.

Change-Id: I01c5f6aaa596fccc1472f5988f431c77ad13820b
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>