e1_input: Fix compiler warning by using offsetof

Use the offsetof/__builtin_offsetof to determine the
offset of a variable inside a structure instead of going
via a NULL pointer and taking the address.

This fixes:
warning: variably modified ‘dummyhalen_offset’ at file scope
1 file changed
tree: 9cd304e5a70e101136c314f3c69ab2bfe1ad3c18
  1. hlrsync/
  2. linux-kernel/
  3. openbsc/
  4. wireshark/