clippy: allow mut_from_ref

The purpose of the function is exactly to change a pointer obtained
from a mutable VolatileSlice into a reference, and doing so is
unsafe.  So just shut up clippy.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Author: bonzini

CHANGELOG.md

@@ -6,6 +6,10 @@
 
 - \[[#327](https://github.com/rust-vmm/vm-memory/pull/327)\] I/O virtual memory support via `IoMemory`, `IommuMemory`, and `Iommu`/`Iotlb`
 
+### Fixed
+
+- \[[#361](https://github.com/rust-vmm/vm-memory/pull/361)\] clippy: allow mut_from_ref
+
 ## \[v0.17.1\]
 
 No visible changes.

src/volatile_memory.rs

@@ -228,6 +228,9 @@ pub trait VolatileMemory {
     ///
     /// If the resulting pointer is not aligned, this method will return an
     /// [`Error`](enum.Error.html).
+    // the function is unsafe, and the conversion is safe if following the safety
+    // instrutions above
+    #[allow(clippy::mut_from_ref)]
     unsafe fn aligned_as_mut<T: ByteValued>(&self, offset: usize) -> Result<&mut T> {
         let slice = self.get_slice(offset, size_of::<T>())?;
         slice.check_alignment(align_of::<T>())?;