staging: rtl8188eu: core: Fix coding style issue

Use %s and  __func__ in place of function names.
This solves following checkpatch.pl warning
WARNING: Prefer using '"%s...", __func__' to using 'rtw_do_join', this function's name, in a string
Signed-off-by: Puranjay Mohan <puranjay12@gmail.com>
Link: https://lore.kernel.org/r/20200701145457.9562-1-puranjay12@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8188eu/core/rtw_ioctl_set.c

@@ -25,7 +25,7 @@ u8 rtw_do_join(struct adapter *padapter)
 	phead = get_list_head(queue);
 	plist = phead->next;
 
-	RT_TRACE(_module_rtl871x_ioctl_set_c_, _drv_info_, ("\n rtw_do_join: phead = %p; plist = %p\n\n\n", phead, plist));
+	RT_TRACE(_module_rtl871x_ioctl_set_c_, _drv_info_, ("\n %s: phead = %p; plist = %p\n\n\n", __func__, phead, plist));
 
 	pmlmepriv->cur_network.join_res = -2;