staging: fsl-mc: section mismatch bug fix

WARNING: drivers/staging/built-in.o(.init.text+0xdc): Section mismatch in reference from the function fsl_mc_bus_driver_init() to the function .exit.text:dprc_driver_exit()
The function __init fsl_mc_bus_driver_init() references
a function __exit dprc_driver_exit().
This is often seen when error handling in the init function
uses functionality in the exit path.
The fix is often to remove the __exit annotation of
dprc_driver_exit() so it may be used outside an exit section.

Signed-off-by: Lijun Pan <Lijun.Pan@freescale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>