x86/platform: tidy do_platform_op() a little

x86/platform: tidy do_platform_op() a little

The function has a few stray scopes and inconsistent use (indentation)
of break statements. Drop the stray braces and bring all the break-s in
line with one another. This in particular means dropping a redundant
break from XENPF_cpu_offline handling, pleasing Misra C:2012 rule 2.1.

No functional change intended.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>