staging: r8188eu: convert _rtw_init_sta_priv() to common error logic

Convert the function _rtw_init_sta_priv() to common kernel error logic.
Return 0 on success and negative value on failure. This is part of
getting rid of returning _SUCCESS and _FAIL which uses inverted error
logic and is used all over the driver.

Signed-off-by: Michael Straube <straube.linux@gmail.com>
Tested-by: Philipp Hortmann <philipp.g.hortmann@gmail.com> # Edimax N150
Link: https://lore.kernel.org/r/20221002074827.8566-6-straube.linux@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>