mfd: Remove __devexit annotation for pm80x_deinit

This fixes below section mismatch warning:

  LD      drivers/mfd/built-in.o
WARNING: drivers/mfd/built-in.o(.devinit.text+0x46c): Section mismatch in reference from the function pm800_probe() to the function .devexit.text:pm80x_deinit()
The function __devinit pm800_probe() references
a function __devexit pm80x_deinit().
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
pm80x_deinit() so it may be used outside an exit section.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>