src not considered as side reg in gadgets like `xchg dst, src`

[845977]

The register src is wrongfully in excluded side regs when side effects are constructed:

rop3/rop3/gadget.py

Lines 62 to 64 in 95f6cb9

	def calculate_side_effects(self) -> None:
	arch = arch_singleton.arch
	excluded = {arch.normalize_reg(r) for r in (self.dst, self.src, arch.sp) if r is not None}

Gadgets like xchg dst, src modify src as side effect.

Suggested fix: remove self.src

[ricardojrdez]

Fixed in #35 (merged as c0fd559).