KVM: SVM: Make set_msr_interception more reliable

set_msr_interception() is used by svm to set up which MSRs should be
intercepted.  It can only fail if someone has changed the code to try
to intercept an MSR without updating the array of ranges.

The return value is ignored anyway: it should just BUG() if it doesn't
work.  (A build-time failure would be better, but that's tricky).

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Avi Kivity <avi@qumranet.com>