ARM: OMAP2+: Fix devexit for smartreflex when CONFIG_HOTPLUG is not set

Otherwise we get:

`omap_sr_remove' referenced in section `.data' of arch/arm/mach-omap2/built-in.o:
defined in discarded section `.devexit.text' of arch/arm/mach-omap2/built-in.o

Signed-off-by: Tony Lindgren <tony@atomide.com>