net: wwan: iosm: fw flashing and cd improvements

1> Function comments moved to .c file.
2> Use literals in return to improve readability.
3> Do error handling check instead of success check.
4> Redundant ret assignment removed.

Signed-off-by: M Chetan Kumar <m.chetan.kumar@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>