UPSTREAM: spi: Drop io_mutex in error paths

A couple of error paths were missing drops of io_mutex.

Reported-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Mark Brown <broonie@kernel.org>
(cherry picked from commit 764f21665a12e99f03124b4c8de722cdbff92213)

BUG=b:62335555
TEST=build and boot

Change-Id: I4d11bcd7db8576e0cab44fc3b3c33bd429c4657a
Signed-off-by: Jeffy Chen <jeffy.chen@rock-chips.com>
Reviewed-on: https://chromium-review.googlesource.com/523886
Commit-Ready: Brian Norris <briannorris@chromium.org>
Reviewed-by: Brian Norris <briannorris@chromium.org>
(cherry picked from commit 0f9cf1de34e72dab2df139b8ad5e9f14481e03ef)
Reviewed-on: https://chromium-review.googlesource.com/537816
Tested-by: Brian Norris <briannorris@chromium.org>