pvmfw: Clarify documentation of flush_region()

Test: -
Change-Id: Ifc8dac5aac173c6f8c24db2e3cf708df3e8d6515
diff --git a/pvmfw/src/helpers.rs b/pvmfw/src/helpers.rs
index ead8bb4..f1ff36d 100644
--- a/pvmfw/src/helpers.rs
+++ b/pvmfw/src/helpers.rs
@@ -63,8 +63,8 @@
     1 << dminline
 }
 
+/// Flush `size` bytes of data cache by virtual address.
 #[inline]
-/// Flush data cache over the entire slice.
 pub fn flush_region(start: usize, size: usize) {
     let line_size = min_dcache_line_size();
     let end = start + size;