gpio: em: do not discard em_gio_irq_domain_cleanup

The newly added gpio-em driver marks its em_gio_irq_domain_cleanup
function as __devexit, which would lead to that function being
discarded in case CONFIG_HOTPLUG is disabled. However, the function
is also called by the error handling logic em_gio_probe, which
would cause a jump into a NULL pointer if it was removed from the
kernel or module.

Without this patch, building kzm9d_defconfig results in:

WARNING: drivers/gpio/built-in.o(.devinit.text+0x330): Section mismatch in reference from the function em_gio_probe() to the function .devexit.text:em_gio_irq_domain_cleanup()
The function __devinit em_gio_probe() references
a function __devexit em_gio_irq_domain_cleanup().
This is often seen when error handling in the init function
uses functionality in the exit path.
The fix is often to remove the __devexit annotation of
em_gio_irq_domain_cleanup() so it may be used outside an exit section.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Magnus Damm <damm@opensource.se>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Rafael J. Wysocki <rjw@sisk.pl>