Revert "isdn: mISDN: Fix potential NULL pointer dereference of kzalloc"

Revert "isdn: mISDN: Fix potential NULL pointer dereference of kzalloc"

This reverts commit b002abe4d55ae5e79c48beb31118e793501f8b91.

Because of recent interactions with developers from @umn.edu, all
commits from them have been recently re-reviewed to ensure if they were
correct or not.

Upon review, this commit was found to be incorrect for the reasons
below, so it must be reverted.  It will be fixed up "correctly" in a
later kernel change.

While it looks like the original change is correct, it is not, as none
of the setup actually happens, and the error value is not propagated
upwards.

Cc: Aditya Pakki <pakki001@umn.edu>
Cc: David S. Miller <davem@davemloft.net>
Link: https://lore.kernel.org/r/20210503115736.2104747-47-gregkh@linuxfoundation.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>