Patch from Ben Dooks

Avoid the possiblity that if the board is using
a 16.9334 or higher crystal with a high PLL
multiplier, then the pll value could overflow
the capability of an int.

Also fix the value types of the intermediate
variables to unsigned int.

Rewrite of patch from Guillaume Gourat
Signed-off-by: NBen Dooks <ben-linux@fluff.org>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>