x86jit: Minor tweaks to asm dispatcher

Shouldn't need protected funcs in the safemem jumps, and can skip right to EAX pretty easily, but with a couple more bytes.  Also shave off the reload of the context pointer each dispatch.

Minimal if any measurable gains, though.

But, I think it's cleaner, and somehow I don't think this line was ever right: `J_CC(CC_NE, asm_.dispatcher, true);`

-[Unknown]