VAX: Fix comment for `*bit<mode>' pattern's peephole

The comment for a peephole provided for the `*bit<mode>' pattern to be
produced in comparison elimination from a sequence involving a bitwise
complement operation of one input operand followed by a bitwise AND
operation between a bitwise complement of said intermediate result and
the other input operand (which corresponds to a sequence of MCOM and BIC
machine instructions) incorrectly refers to the first operation as MNEG
(which is the machine instruction for arithmetic negation) rather than
MCOM as it is supposed to.  Fix it.

	gcc/
	* config/vax/vax.md: Fix comment for `*bit<mode>' pattern's
	peephole.