staging: ste_rmi4: avoid unused function warnings

The rmi4 touchscreen driver encloses the power-management
functions in #ifdef CONFIG_PM, but the smtcfb_pci_suspend/resume
functions are only really used when CONFIG_PM_SLEEP is also
set, as a frequent gcc warning shows:

ste_rmi4/synaptics_i2c_rmi4.c:1050:12: warning: 'synaptics_rmi4_suspend' defined but not used
ste_rmi4/synaptics_i2c_rmi4.c:1084:12: warning: 'synaptics_rmi4_resume' defined but not used

This changes the driver to remove the #ifdef and instead mark
the functions as __maybe_unused, which is a nicer anyway, as it
provides build testing for all the code in all configurations
and is harder to get wrong.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>