powerpc/macintosh: Fix __devexit annotation in rack-meter.c

powerpc/macintosh: Fix __devexit annotation in rack-meter.c

The following warning was seen building rack-meter.c

WARNING: drivers/built-in.o(.text+0xac784): Section mismatch in reference from the function rackmeter_shutdown() to the function .devexit.text:rackmeter_stop_cpu_sniffer()
The function rackmeter_shutdown() references a function in an exit section.
Often the function rackmeter_stop_cpu_sniffer() has valid usage outside the exit section
and the fix is to remove the __devexit annotation of rackmeter_stop_cpu_sniffer.

This patch resolves the warning by removing the __devexit annotation from
rackmeter_stop_cpu_sniffer().

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Cc: linuxppc-dev@lists.ozlabs.org
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>