spi: stm32-qspi: Fix unbalanced pm_runtime_enable issue

spi: stm32-qspi: Fix unbalanced pm_runtime_enable issue

Issue detected by unbinding/binding the stm32 qspi driver as following:

root@stm32mp2:~# echo 40430000.spi > /sys/bus/platform/drivers/stm32-qspi/404300
00.spi/driver/unbind
root@stm32mp2:~# echo 40430000.spi > /sys/bus/platform/drivers/stm32-qspi/bind
[  969.864021] stm32-qspi 40430000.spi: Unbalanced pm_runtime_enable!
[  970.225161] spi-nor spi0.0: mx66u51235f (65536 Kbytes)
[  970.935721] spi-nor spi0.1: mx66u51235f (65536 Kbytes)

Fixes: 9d282c17b023 ("spi: stm32-qspi: Add pm_runtime support")

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Link: https://lore.kernel.org/r/20200429102625.25974-1-patrice.chotard@st.com
Signed-off-by: Mark Brown <broonie@kernel.org>