DOC: fix typo in documentation of vecmat

The body of the summary uses the symbol v to reference the `x1`
parameter, however in the displayed math, b is used instead. This commit
changes b to v in the displayed math for concistency.

Author: Mojert

numpy/_core/code_generators/ufunc_docstrings.py

@@ -3030,7 +3030,7 @@ def add_newdoc(place, name, doc):
     vector-matrix product is defined as:
 
     .. math::
-       \\mathbf{b} \\cdot \\mathbf{A} = \\sum_{i=0}^{n-1} \\overline{v_i}A_{ij}
+       \\mathbf{v} \\cdot \\mathbf{A} = \\sum_{i=0}^{n-1} \\overline{v_i}A_{ij}
 
     where the sum is over the last dimension of ``x1`` and the one-but-last
     dimensions in ``x2`` (unless `axes` is specified) and where