of/rtc: rtc-mpc5121.c: Fix build failures

    
Fixes build errors caused by the:
- OF device_node pointer being moved into struct device
- removal of the match_table field from struct of_platform_driver

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
CC: Paul Gortmaker <p_gortmaker@yahoo.com>
CC: Alessandro Zummo <a.zummo@towertech.it>
CC: Wolfgang Denk <wd@denx.de>
CC: Tejun Heo <tj@kernel.org>
CC: Anatolij Gustschin <agust@denx.de>
CC: rtc-linux@googlegroups.com
CC: devicetree-discuss@lists.ozlabs.org