saa716x: Fix errors and improve saa716x_set_clk

- Use stretched clock also for 125 MHz as its active for default 125 MHz clocks.
- Fix not setting MSUB in clock divider.
- Sleep for 10 us instead of 10 ms.
- Fix typo in condition.

Signed-off-by: Andreas Regel <andreas.regel@gmx.de>

Credits: powARman
Merge pull request #46 from bas-t/fixes

saa716x: Fix errors and improve saa716x_set_clk