The f75375s driver crashes the kernel if it detects an an internal
implementation error. While the detected conditions suggest that
there is a bug in the code, the condition is not fatal.
Replace BUG() with WARN().

Cc: Riku Voipio <riku.voipio@iki.fi>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>