clk: si5341: Avoid divide errors due to bogus register contents

clk: si5341: Avoid divide errors due to bogus register contents

If the Si5341 is being initially programmed and has no stored NVM
configuration, some of the register contents may contain unexpected
values, such as zeros, which could cause divide by zero errors during
driver initialization. Trap errors caused by zero registers or zero clock
rates which could result in divide errors later in the code.

Fixes: efc8b8846d ("clk: Add Si5341/Si5340 driver")
Signed-off-by: Robert Hancock <robert.hancock@calian.com>
Link: https://lore.kernel.org/r/20210325192643.2190069-4-robert.hancock@calian.com
Signed-off-by: Stephen Boyd <sboyd@kernel.org>