Add missing close to MSR register open fd

[mimir-d]

• there are usecases where this missing close leads to fd exhaustion

testing:

% go test   
PASS
ok      github.com/9elements/converged-security-suite/v2/pkg/registers  0.289sw

[rihter007]

The linter is right, in this case we theoretically can get a panic.

Also may be it makes sense to put the whole content of the for to a separate function to avoid defer-ing in a loop. But this is a nitpicking. Feel free to ignore :)

I guess once can use inplace function for it:

for i := 0; i < runtime.NumCPU(); i++ { func() { ... defer msr.Close() ... }() }

[mimir-d]

i could've sworn i put that defer after the error check. fixing...