bpf, arm32: correct check_imm24

imm24 is signed, so the right range is:

  [-(1<<(24 - 1)), (1<<(24 - 1)) - 1]

Note: this patch also fix a typo.

Fixes: 39c13c20

 ("arm: eBPF JIT compiler")
Signed-off-by: Wang YanQing <udknight@gmail.com>
Cc: Shubham Bansal <illusionist.neo@gmail.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux@armlinux.org.uk
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>