Xen: fix braces and tabs coding style issue in xenbus_probe.c

This is a patch to the xenbus_probe.c file that fixed up braces and tabs 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>