We were consuming the values returned from `GetPinnedReference()` API, however
`.Consume()` uses `volatile` and that introduces memory barriers for ARM64.
Since we just want to measure the performance of `GetPinnedReference()` it is
unnecessary to introduce a differentiating factor for 1 architecture and not the
other. Hence I have removed the `.Consume()` and instead just storing the returned
result in a variable.

Before:
```asm
...
G_M52573_IG23:
        79400063          ldrh    w3, [x3]
        D5033BBF          dmb     ish
        79008023          strh    w3, [x1,dotnet#64]
        D2800003          mov     x3, #0
        34000040          cbz     w0, G_M52573_IG25
                                                ;; bbWeight=1    PerfScore 15.50
G_M52573_IG24:
        AA0203E3          mov     x3, x2
                                                ;; bbWeight=0.25 PerfScore 0.13
G_M52573_IG25:
        79400063          ldrh    w3, [x3]
        D5033BBF          dmb     ish
        79008023          strh    w3, [x1,dotnet#64]
        D2800003          mov     x3, #0
        34000040          cbz     w0, G_M52573_IG27
                                                ;; bbWeight=1    PerfScore 15.50
G_M52573_IG26:
        AA0203E3          mov     x3, x2
                                                ;; bbWeight=0.25 PerfScore 0.13
...

```

After
```asm
...
G_M51552_IG23:
        79400021          ldrh    w1, [x1]
        D2800001          mov     x1, #0
        34000040          cbz     w0, G_M51552_IG25
                                                ;; bbWeight=1    PerfScore 4.50
G_M51552_IG24:
        AA0203E1          mov     x1, x2
                                                ;; bbWeight=0.25 PerfScore 0.13
G_M51552_IG25:
        79400021          ldrh    w1, [x1]
        D2800001          mov     x1, #0
        34000040          cbz     w0, G_M51552_IG27
                                                ;; bbWeight=1    PerfScore 4.50
G_M51552_IG26:
        AA0203E1          mov     x1, x2
                                                ;; bbWeight=0.25 PerfScore 0.13
...

```

This change reduces the ARM64 numbers for this benchmark from 10ns to 1ns. I am not sure if
we should just add `Consume()` method and mark it as `NoInline`. That's what is done for
`System.Memory.Span<T>.GetPinnedReference()` benchmark.