cmd/vet/all: add bitwidths for mips and mipsle

cmd/vet/all still doesn't run for mips/mipsle,
because the rest of the toolchain doesn't yet
fully support it.

Change-Id: I1a86b0edddbdcd5f43e752208508d99da7aabbb3
Reviewed-on: https://go-review.googlesource.com/33134
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>

src/cmd/vet/all/main.go

@@ -321,6 +321,8 @@ var nbits = map[string]int{
 	"amd64p32": 32,
 	"arm":      32,
 	"arm64":    64,
+	"mips":     32,
+	"mipsle":   32,
 	"mips64":   64,
 	"mips64le": 64,
 	"ppc64":    64,