Fix following section mismatch warnings in acpi

WARNING: drivers/acpi/asus_acpi.o(.init.text+0xb7): Section mismatch: reference to .exit.text: (after 'init_module')
WARNING: o-i386/drivers/acpi/toshiba_acpi.o(.init.text+0x13a): Section mismatch: reference to .exit.text: (after 'init_module')

The exit function is used in the init function during an error codition.
As __exit may be discarded during link-time / run-time this is no good.
Do not mark the exit function __exit.

Note: This warning is only seen by my local copy of modpost
      but the change will soon hit upstream.
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Len Brown <lenb@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>