[doc] Fix typos in MINLOC, MAXLOC documentation

[doc] Fix typos in MINLOC, MAXLOC documentation

I think there's a typo in the documentation of the MINLOC and MAXLOC intrinsics.
It implies that when the BACK argument is true it returns the first occurrence of the min/max value,
but my understanding is that it should return the last occurrence.

This patch fixes the documentation.

	* intrinsic.texi (MINLOC): Fix typo in BACK argument documentation.
	(MAXLOC): Likewise.

From-SVN: r269906