nfp: bpf: make array exp_mask static, makes object smaller

Don't populate the array exp_mask on the stack but instead make it
static. Makes the object code smaller by 224 bytes.

Before:
   text	   data	    bss	    dec	    hex	filename
  77832	   2290	      0	  80122	  138fa	ethernet/netronome/nfp/bpf/jit.o

After:
   text	   data	    bss	    dec	    hex	filename
  77544	   2354	      0	  79898	  1381a	ethernet/netronome/nfp/bpf/jit.o

(gcc version 9.2.1, amd64)
Signed-off-by: NColin Ian King <colin.king@canonical.com>
Acked-by: NJakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: NJakub Kicinski <jakub.kicinski@netronome.com>

drivers/net/ethernet/netronome/nfp/bpf/jit.c

@@ -3952,7 +3952,7 @@ static void nfp_bpf_opt_neg_add_sub(struct nfp_prog *nfp_prog)
 static void nfp_bpf_opt_ld_mask(struct nfp_prog *nfp_prog)
 {
 	struct nfp_insn_meta *meta1, *meta2;
-	const s32 exp_mask[] = {
+	static const s32 exp_mask[] = {
 		[BPF_B] = 0x000000ffU,
 		[BPF_H] = 0x0000ffffU,
 		[BPF_W] = 0xffffffffU,