msun: correct comment

The comment in msun/src/e_jn.c lacks proper grammar, and is incorrect on
the choice of normalization entity.

PR:	266503
MFC after:	3 days

lib/msun/src/e_jn.c

@@ -22,15 +22,15 @@ __FBSDID("$FreeBSD$");
  *	y0(0)=y1(0)=yn(n,0) = -inf with division by zero signal;
  *	y0(-ve)=y1(-ve)=yn(n,-ve) are NaN with invalid signal.
  * Note 2. About jn(n,x), yn(n,x)
- *	For n=0, j0(x) is called,
- *	for n=1, j1(x) is called,
- *	for n<x, forward recursion us used starting
+ *	For n=0, j0(x) is called.
+ *	For n=1, j1(x) is called.
+ *	For n<x, forward recursion is used starting
  *	from values of j0(x) and j1(x).
- *	for n>x, a continued fraction approximation to
+ *	For n>x, a continued fraction approximation to
  *	j(n,x)/j(n-1,x) is evaluated and then backward
  *	recursion is used starting from a supposed value
- *	for j(n,x). The resulting value of j(0,x) is
- *	compared with the actual value to correct the
+ *	for j(n,x). The resulting values of j(0,x) or j(1,x) are
+ *	compared with the actual values to correct the
  *	supposed value of j(n,x).
  *
  *	yn(n,x) is similar in all respects, except