iwlegacy: make const array static to shink object code size
Don't populate const array ac_to_fifo on the stack in an inlined
function, instead make it static. Makes the object code smaller
by over 800 bytes:
text data bss dec hex filename
159029 33154 1216 193399 2f377 4965-mac.o
text data bss dec hex filename
158122 33250 1216 192588 2f04c 4965-mac.o
(gcc version 7.2.0 x86_64)
Signed-off-by: Colin Ian King <colin.king@canonical.com> Acked-by: Stanislaw Gruszka <sgruszka@redhat.com> Signed-off-by: Kalle Valo <kvalo@codeaurora.org>