Revert "usb: host: xhci: Increase number of event ring segments to 4"

'Commit 980e3a90 ("usb: host: xhci: Increase number of event
ring segments to 4")' is leading to xHC taking more time to
process the queued TDs and cleanup, thereby increasing the HALT
time. Revert the commit to go back to original times.
The Ring Full Error events can be cleaned up by decreasing number
of URBs being queued.

Change-Id: I3058d755b0dc526ab35d0cf165d37f2cb8019dd2
Signed-off-by: Ajay Agarwal <ajaya@codeaurora.org>