drm/xe/sa: Tidy up coding style in init()

There is no need to use tile_to_xe() since we already got the xe.
And we should keep all variable declarations together, no need for
separate sa_manager declaration.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241220194205.995-5-michal.wajdeczko@intel.com