ntlm: Use 'CURLcode result'

Continuing commit 0eb3d15ccb more return code variable name changes.
ntlm: Return CURLcode from Curl_ntlm_core_mk_lm_hash()
ntlm: Return all errors from Curl_ntlm_core_mk_nt_hash()

For consistency with other areas of the NTLM code propagate all errors
from Curl_ntlm_core_mk_nt_hash() up the call stack rather than just
CURLE_OUT_OF_MEMORY.