Fix typo in documentation of gstrs

[maxaehle]

The documentation of dgscon gives conflicting information about how its input arguments L and U have to be computed:

• In the main text, it refers to a function DGETRF which, to my knowledge, does not exist in SuperLU.
• In the description of the arguments, it refers to dgstrf.

The proposed change replaces DGETRF by DGSTRF in the comments in the code. It seems that the html documentation are also part of the repo, and would therefore need to be rebuilt.

As a side question, I was wondering if it is possible to use dgscon with an incomplete LU decomposition formed by dgsitrf?

I'm interested because I'm currently trying to extend the SciPy wrapper for SuperLU in response to scipy/scipy#18969.

[xiaoyeli]

Thanks. I'll update doxygen document separately.
Regarding your question with ILU: condition estimation needs accurate LU decomposition. ILU would not be useful for this.