Description of FNMADD and FNMSUB is swapped

[vineetgarc]

Per ISA spec:

FNMSUB.S multiplies the values in rs1 and rs2, negates the product, adds the value in rs3, and
writes the final result to rd. FNMSUB.S computes -(rs1×rs2)+rs3.
FNMADD.S multiplies the values in rs1 and rs2, negates the product, subtracts the value in rs3,
and writes the final result to rd. FNMADD.S computes -(rs1×rs2)-rs3.
..
The FNMSUB and FNMADD instructions are counterintuitively named, owing to the naming
of the corresponding instructions in MIPS-IV.