mmc: renesas-sdhi: Refactor probe function

Move the assignment of priv->quirks earlier in the function. This allows
us to drop the quirks local variable and makes it easier to maintain
clean error handling when we add RZ/G2L support in the next patch.

Signed-off-by: Paul Barker <paul.barker.ct@bp.renesas.com>
Reviewed-by: Marek Vasut <marek.vasut+renesas@mailbox.org>