[POWERPC] typo fix and whitespace cleanup on mpc52xx-uart driver

Single typo fix and whitespace changes.  In preparation for heavy
changes to this driver when support for arch/powerpc is added.
Since the driver will be changing significantly anyway, then may
as well take the opportunity to clean it up first.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>