Clean up the param checking, removing some code paths that will never
happen.

Signed-off-by: Nathan Rossi <nathan@nathanrossi.com>
Cc: Michal Simek <michal.simek@xilinx.com>
Cc: Tom Rini <trini@konsulko.com>
Reported-by: Coverity (CID 133251)
Reviewed-by: Tom Rini <trini@konsulko.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>