staging: wlan-ng: fix exit return when sme->key_idx >= NUM_WEPKEYS

staging: wlan-ng: fix exit return when sme->key_idx >= NUM_WEPKEYS

Currently the exit return path when sme->key_idx >= NUM_WEPKEYS is via
label 'exit' and this checks if result is non-zero, however result has
not been initialized and contains garbage.  Fix this by replacing the
goto with a return with the error code.

Addresses-Coverity: ("Uninitialized scalar variable")
Fixes: 0ca6d8e74489 ("Staging: wlan-ng: replace switch-case statements with macro")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20191014110201.9874-1-colin.king@canonical.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>