pinctrl: single: Fix missing flush of posted write for a wakeirq

pinctrl: single: Fix missing flush of posted write for a wakeirq

[ Upstream commit 0ac3c0a4025f41748a083bdd4970cb3ede802b15 ]

With many repeated suspend resume cycles, the pin specific wakeirq
may not always work on omaps. This is because the write to enable the
pin interrupt may not have reached the device over the interconnect
before suspend happens.

Let's fix the issue with a flush of posted write with a readback.

Cc: stable@vger.kernel.org
Reported-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>