Cranelift: simplify DataValue::eq

[dev-er1]

This simplifies the PartialEq implementation for DataValue by replacing the repeated ... => false match arms with a single wildcard arm.

No functional changes intended.

[cfallin]

Thanks! Happy to merge once the rustfmt issue is fixed.

[alexcrichton]

One possible note here is that this is an intentional idiom you'll find throughout Wasmtime in a number of places. The intentional part is that if a new variant is added the compiler's exhaustive-match checks flag the match as "gotta add more arms here". With a catch-all like proposed in this PR adding a new variant will get no such warnings and it'd be some bug later own down the road to force adding the match. Personally I find that more valuable than removing lines, but that's also a subjective call

[cfallin]

Ah, yeah, sorry, I should've registered that here -- brain saw wildcard -> wildcard and I missed that. Thanks; @dev-er1 we'll close this as above.

[dev-er1]

In any case, thanks for the review.