sspi.c: Post Curl_sspi_version() rework code tidy up

Removed duplicate blank lines.
Removed spaces between the not and test in various if statements.
Removed explicit test of NULL in an if statement.
Placed function returns on same line as function declarations.
Replaced the use of curl_maprintf() with aprintf() as it is the
preprocessor job to do this substitution if ENABLE_CURLX_PRINTF
is set.