[POWERPC] mpc5200: Cleanup checkpatch.pl problems in mpc52xx_uart.c

In preparation of adding MPC5121 support
cleanup some things that checkpatch.pl complains
about also some minor fixes suggested by
Stephen Rothwell.
Signed-off-by: John Rigby <jrigby@freescale.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>