The _rtw_enqueue_cmd function is called only by rtw_enqueue_cmd.

When _rtw_enqueue_cmd is called, the caller has already checked that the
obj parameter is not NULL. _rtw_enqueue_cmd returns _SUCCESS in any case.

We can merge the two functions and simplify the error handling.
Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Tested-by: Philipp Hortmann <philipp.g.hortmann@gmail.com> # Edimax N150
Link: https://lore.kernel.org/r/20230211165045.414424-1-martin@kaiser.cxSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>