Xen: fix whitespaces,tabs coding style issue in drivers/xen/events.c

This is a patch to the events.c file that fixed up
whitespaces, tabs and braces errors found by the
checkpatch.pl tools.

Signed-off-by: Ruslan Pisarev <ruslan@rpisarev.org.ua>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>