wimax: fix gcc warnings in sh4 when calling BUG()

SH4's BUG() seems to confuse the compiler as it is considered to
return; thus, some functions would trigger usage of uninitialized
variables or non-void functions returning void.

Work around by initializing/returning.

Signed-off-by: Inaky Perez-Gonzalez <inaky@linux.intel.com>