rust: io_mem.rs: improve IoMem's docstring

IoMem's docstring currently states that const generic SIZE specifies an
address's size. More precisely, it specifies the size of the memory area
the address points to.

Improve the wording.

Signed-off-by: Philipp Stanner <[email protected]>
Signed-off-by: Andreas Hindborg <[email protected]>

Author: Philipp Stanner

rust/kernel/io_mem.rs

@@ -34,8 +34,9 @@ impl Resource {
 ///
 /// # Invariants
 ///
-/// `ptr` is a non-null and valid address of at least `SIZE` bytes and returned by an `ioremap`
-/// variant. `ptr` is also 8-byte aligned.
+/// `ptr` is a non-null and valid address of a memory area of a length of at
+/// least `SIZE` bytes. It is returned by an `ioremap` variant. `ptr` is also
+/// 8-byte aligned.
 ///
 /// # Examples
 ///