[LangRef] Fix sphinx label syntax

Author: felipepiovezan

llvm/docs/LangRef.rst

@@ -6008,7 +6008,7 @@ The current supported opcode vocabulary is limited:
 
   Because ``DW_OP_LLVM_entry_value`` is defined in terms of registers, it is
   usually used in MIR, but it is also allowed in LLVM IR when targetting a
-  :ref:`_swiftasync` argument. The operation is introduced by:
+  :ref:`swiftasync <swiftasync>` argument. The operation is introduced by:
 
     - ``LiveDebugValues`` pass, which applies it to function parameters that
       are unmodified throughout the function. Support is limited to simple
@@ -6019,8 +6019,9 @@ The current supported opcode vocabulary is limited:
       (``DW_AT_call_site_parameter_value``) is represented as entry value of
       the parameter.
     - ``CoroSplit`` pass, which may move variables from allocas into a
-      coroutine frame. If the coroutine frame is a :ref:`_swiftasync` argument,
-      the variable is described with an ``DW_OP_LLVM_entry_value`` operation.
+      coroutine frame. If the coroutine frame is a
+      :ref:`swiftasync <swiftasync>` argument, the variable is described with
+      an ``DW_OP_LLVM_entry_value`` operation.
 
 - ``DW_OP_LLVM_arg, N`` is used in debug intrinsics that refer to more than one
   value, such as one that calculates the sum of two registers. This is always