mwifiex: scan: simplify dereference of bss_desc fields

given this structure:
struct foo {
  struct bar {
     int baz;
  }
}

these accesses are equivalent:
(*(foo->bar)).baz
foo->bar->baz

Signed-off-by: Andreas Fenkart <afenkart@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>