staging: wilc1000: refactor wilc_wlan_handle_isr_ext to avoid goto statement

Refactor wilc_wlan_handle_isr_ext() to avoid the use of the goto label.
Also avoid the unnecessary NULL check for 'wilc->rx_buffer' and
calling wilc_wlan_handle_rxq() only after wilc_wlan_rxq_add() call.
The link [1] contains details for discussion related to this changes.

[1]. https://patchwork.kernel.org/patch/10533601/



Signed-off-by: Ajay Singh <ajay.kathat@microchip.com>
Suggested-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>