EDAC, mpc85xx: Silence unused variable warning

EDAC, mpc85xx: Silence unused variable warning

We were getting this build warning:

  drivers/edac/mpc85xx_edac.c:1247:6: warning: unused variable 'pvr'

pvr is only used if CONFIG_FSL_SOC_BOOKE is defined. Declare it
__maybe_unused.

Suggested-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Cc: linux-edac <linux-edac@vger.kernel.org>
Link: http://lkml.kernel.org/r/1454427573-7994-1-git-send-email-sudipm.mukherjee@gmail.com
Signed-off-by: Borislav Petkov <bp@suse.de>