Update col index to j in sparse docs (#32787)

* fix fortran ccall example (#32784)

* same update as PR #32769

Author: magerton

stdlib/SparseArrays/docs/src/index.md

@@ -20,7 +20,7 @@ row indices. The internal representation of `SparseMatrixCSC` is as follows:
 struct SparseMatrixCSC{Tv,Ti<:Integer} <: AbstractSparseMatrix{Tv,Ti}
     m::Int                  # Number of rows
     n::Int                  # Number of columns
-    colptr::Vector{Ti}      # Column i is in colptr[i]:(colptr[i+1]-1)
+    colptr::Vector{Ti}      # Column j is in colptr[j]:(colptr[j+1]-1)
     rowval::Vector{Ti}      # Row indices of stored values
     nzval::Vector{Tv}       # Stored values, typically nonzeros
 end

stdlib/SparseArrays/src/sparsematrix.jl

@@ -176,10 +176,10 @@ column. In conjunction with [`nonzeros`](@ref) and
     rows = rowvals(A)
     vals = nonzeros(A)
     m, n = size(A)
-    for i = 1:n
-       for j in nzrange(A, i)
-          row = rows[j]
-          val = vals[j]
+    for j = 1:n
+       for i in nzrange(A, j)
+          row = rows[i]
+          val = vals[i]
           # perform sparse wizardry...
        end
     end