i2c: rcar: enable interrupts before starting transfer

We want to enable the interrupts _before_ starting the transfer because
it is good programming style and also the proposed order in the R-Car
manual. There is no difference in practice because it doesn't matter in
which order both conditions appear if we wait for both to happen.

Signed-off-by: Ryo Kataoka <ryo.kataoka.wt@renesas.com>
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Ulrich Hecht <uli+renesas@fpond.eu>
Signed-off-by: Wolfram Sang <wsa@kernel.org>