Fix big endian issue in Interlocked test cases (#101429)

Fix big indian issue wiht BitConverted as part of intercloked test cases.
These were causing failures in runtime_community pipeline

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Co-authored-by: root <root@t8375036.lnxero1.boe>

src/libraries/System.Private.CoreLib/src/System/Threading/Interlocked.cs

@@ -126,7 +126,7 @@ public static unsafe ushort Exchange(ref ushort location1, ushort value)
             nuint offset = Unsafe.OpportunisticMisalignment(ref location1, sizeof(uint));
             ref uint alignedRef = ref Unsafe.As<ushort, uint>(ref Unsafe.SubtractByteOffset(ref location1, offset));
             int bitOffset =
-                (int)((BitConverter.IsLittleEndian ? offset : sizeof(uint) - offset - sizeof(byte)) * 8); // to bit offset
+                (int)((BitConverter.IsLittleEndian ? offset : sizeof(uint) - offset - sizeof(ushort)) * 8); // to bit offset
             Debug.Assert(bitOffset is 0 or 16);
             uint mask = ~((uint)ushort.MaxValue << bitOffset);
             uint shiftedValue = (uint)value << bitOffset;
@@ -308,7 +308,7 @@ public static unsafe ushort CompareExchange(ref ushort location1, ushort value,
             nuint offset = Unsafe.OpportunisticMisalignment(ref location1, sizeof(uint));
             ref uint alignedRef = ref Unsafe.As<ushort, uint>(ref Unsafe.SubtractByteOffset(ref location1, offset));
             int bitOffset =
-                (int)((BitConverter.IsLittleEndian ? offset : sizeof(uint) - offset - sizeof(byte)) * 8); // to bit offset
+                (int)((BitConverter.IsLittleEndian ? offset : sizeof(uint) - offset - sizeof(ushort)) * 8); // to bit offset
             Debug.Assert(bitOffset is 0 or 16);
             uint mask = ~((uint)ushort.MaxValue << bitOffset);
             uint shiftedValue = (uint)value << bitOffset;