[spec] Fixed typos regarding blocktypes (#1941)

Author: 4y8

document/core/valid/instructions.rst

@@ -2015,7 +2015,7 @@ Control Instructions
 :math:`\LOOP~\blocktype~\instr^\ast~\END`
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-* The :ref:`block type <syntax-blocktype>` must be :ref:`valid <valid-blocktype>` as some :ref:`instruction type <syntax-functype>` :math:`[t_1^\ast] \to_{x^\ast} [t_2^\ast]`.
+* The :ref:`block type <syntax-blocktype>` must be :ref:`valid <valid-blocktype>` as some :ref:`instruction type <syntax-instrtype>` :math:`[t_1^\ast] \to [t_2^\ast]`.
 
 * Let :math:`C'` be the same :ref:`context <context>` as :math:`C`, but with the :ref:`result type <syntax-resulttype>` :math:`[t_1^\ast]` prepended to the |CLABELS| vector.
 
@@ -2075,7 +2075,7 @@ Control Instructions
 :math:`\TRYTABLE~\blocktype~\catch^\ast~\instr^\ast~\END`
 .........................................................
 
-* The :ref:`block type <syntax-blocktype>` must be :ref:`valid <valid-blocktype>` as some :ref:`function type <syntax-functype>` :math:`[t_1^\ast] \to [t_2^\ast]`.
+* The :ref:`block type <syntax-blocktype>` must be :ref:`valid <valid-blocktype>` as some :ref:`instruction type <syntax-instrtype>` :math:`[t_1^\ast] \to [t_2^\ast]`.
 
 * For every :ref:`catch clause <syntax-catch>` :math:`\catch_i` in :math:`\catch^\ast`, :math:`\catch_i` must be :ref:`valid <valid-catch>`.