spi: spi-mem: stm32-qspi: stm32_qspi_pm_ops can be static

Fixes: 2e541b64

 ("spi: spi-mem: stm32-qspi: add suspend/resume support")
Signed-off-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>