drivers/dahdi: fix always true cond

Remove these checks as they are not useful. For example, wc->xb gets
allocated together with wc. With these removed, the code behaves the
same as before.

Fix for these warnings with current linux master:

wcte43x-base.c: In function 't43x_init_one':
wcte43x-base.c:3517:13: warning: the comparison will always evaluate as 'true' for the address of 'xb' will never be NULL [-Waddress]
 3517 |         if (&wc->xb)
      |             ^
wcte43x-base.c:141:21: note: 'xb' declared here
  141 |         struct wcxb xb;
      |                     ^~

xpp/xbus-core.c: In function 'xbus_check_unique':
xpp/xbus-core.c:116:13: warning: the comparison will always evaluate as 'true' for the address of 'label' will never be NULL [-Waddress]
  116 |         if (xbus->label && *(xbus->label)) {
      |             ^~~~

etc.

Change-Id: I33ee446a32de3bb8d9fe966a2989994bf4bbd806
---
M drivers/dahdi/dahdi-base.c
M drivers/dahdi/dahdi_dynamic_ethmf.c
M drivers/dahdi/wcte13xp-base.c
M drivers/dahdi/wcte43x-base.c
M drivers/dahdi/xpp/xbus-core.c
5 files changed, 7 insertions(+), 15 deletions(-)