spi: omap2-mcspi: Remove unnecessary pm_runtime_force_suspend()

Commit 5a686b2c ("spi: omap2-mcspi: Idle hardware during suspend
and resume") added calls for pm_runtime_force_suspend() and
pm_runtime_force_resume() to make sure spi is idled between
device_prepare() and device_complete().

But testing Linux next, I now noticed that we will get the following:

spi_master spi0: Failed to power device: -13

Looking at things more turns out we can just remove this non-standard
code. I was probably testing with some extra experimental patches
earlier when I thought we need pm_runtime_force_suspend() and
pm_runtime_force_resume().

Fixes: 5a686b2c ("spi: omap2-mcspi: Idle hardware during suspend
and resume")
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Mark Brown <broonie@kernel.org>