ath9k: make const array reg_hole_list static, reduces object code size

Don't populate the read-only array reg_hole_list on the stack, instead make
it static.  Makes the object code smaller by over 200 bytes:

Before:
   text	   data	    bss	    dec	    hex	filename
  57518	  15248	      0	  72766	  11c3e	debug.o

After:
   text	   data	    bss	    dec	    hex	filename
  57218	  15344	      0	  72562	  11b72	debug.o

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>