i965/vec4: Reswizzle sources when necessary.

i965/vec4: Reswizzle sources when necessary.

Despite the comment above the function claiming otherwise, the function
did not reswizzle sources, which would lead to bad code generation since
commit 04895f5c, which began claiming we could do such swizzling when we
could not.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=82932
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>