iwlwifi: mvm: isolate the get nvm flow

This will soon be a bit more complicated. Take it out
to a function.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20210210171218.431f31a86ea0.I9db96647eb9c7142051e26cd5be3f52c5ffc5534@changeid


Signed-off-by: Luca Coelho <luciano.coelho@intel.com>