mmc: tmio: refactor set_clock a little

Some of the indentation made the code awful to read. Fix that. Also,
introduce defines instead of magic hex values. Note that this includes
one change: We mask out know 0xff instead of 0x1ff. But 0x100 has always
been the clock enable bit. It doesn't make any sense to set it depending
on the clock calculation. Update copyright notices, too. I'll be working
on those files some more in the future.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>