i965/fs: Use a const reference in fs_reg::equals instead of a pointer.

i965/fs: Use a const reference in fs_reg::equals instead of a pointer.

This lets you omit some ampersands and is more idiomatic C++.  Using
const also marks the function as not altering either register (which
was obvious, but nice to enforce).

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>