wimax/i2400m: Remove VLAIS

Convert Variable Length Array in Struct (VLAIS) to valid C by converting
local struct definition to use a flexible array. The structure is only
used to define a cast of a buffer so the size of the struct is not used
to allocate storage.

Signed-off-by: Behan Webster <behanw@converseincode.com>
Signed-off-by: Mark Charebois <charlebm@gmail.com>
Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Signed-off-by: David S. Miller <davem@davemloft.net>