Fix too_long_first_doc_paragraph clippy warning

Solves:
https://rust-lang.github.io/rust-clippy/master/index.html#too_long_first_doc_paragraph

Change-Id: I790b60c3d8c49c46e98b2f045d382820e20dd774
Signed-off-by: Tomás González <tomasagustin.gonzalezorlando@arm.com>
diff --git a/src/lib.rs b/src/lib.rs
index dc965ef..0328a82 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -417,8 +417,10 @@
 pub struct DirectMsg2Args([u64; 14]);
 
 /// Descriptor for a dynamically allocated memory buffer that contains the memory transaction
-/// descriptor. Used by `FFA_MEM_{DONATE,LEND,SHARE,RETRIEVE_REQ}` interfaces, only when the TX
-/// buffer is not used to transmit the transaction descriptor.
+/// descriptor.
+///
+/// Used by `FFA_MEM_{DONATE,LEND,SHARE,RETRIEVE_REQ}` interfaces, only when the TX buffer is not
+/// used to transmit the transaction descriptor.
 #[derive(Debug, Eq, PartialEq, Clone, Copy)]
 pub enum MemOpBuf {
     Buf32 { addr: u32, page_cnt: u32 },
@@ -439,9 +441,10 @@
     Reg64([u64; 16]),
 }
 
-/// FF-A "message types", the terminology used by the spec is "interfaces". The interfaces are used
-/// by FF-A components for communication at an FF-A instance. The spec also describes the valid FF-A
-/// instances and conduits for each interface.
+/// FF-A "message types", the terminology used by the spec is "interfaces".
+///
+/// The interfaces are used by FF-A components for communication at an FF-A instance. The spec also
+/// describes the valid FF-A instances and conduits for each interface.
 #[derive(Debug, Eq, PartialEq, Clone, Copy)]
 pub enum Interface {
     Error {