bpf: arm64: fix uninitialized variable

fix the following issue:
arch/arm64/net/bpf_jit_comp.c: In function 'bpf_int_jit_compile':
arch/arm64/net/bpf_jit_comp.c:982:18: error: 'image_size' may be used
uninitialized in this function [-Werror=maybe-uninitialized]

Fixes: db496944 ("bpf: arm64: add JIT support for multi-function programs")
Reported-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

arch/arm64/net/bpf_jit_comp.c

@@ -897,6 +897,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
 		image_ptr = jit_data->image;
 		header = jit_data->header;
 		extra_pass = true;
+		image_size = sizeof(u32) * ctx.idx;
 		goto skip_init_ctx;
 	}
 	memset(&ctx, 0, sizeof(ctx));