i2c: ocores: set IACK bit after core is enabled

[ Upstream commit 5a72477273066b5b357801ab2d315ef14949d402 ]

Setting IACK bit when core is disabled does not clear the "Interrupt Flag"
bit in the status register, and the interrupt remains pending.

Sometimes it causes failure for the very first message transfer, that is
usually a device probe.

Hence, set IACK bit after core is enabled to clear pending interrupt.

Fixes: 18f98b1e ("[PATCH] i2c: New bus driver for the OpenCores I2C controller")
Signed-off-by: Grygorii Tertychnyi <grygorii.tertychnyi@leica-geosystems.com>
Acked-by: Peter Korsgaard <peter@korsgaard.com>
Cc: stable@vger.kernel.org
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
(cherry picked from commit 1f7e4dd58af1267db2970e5c2e98a4d0ff170047)
Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>