Fix the warnings

  arch/m68k/mac/macboing.c: In function 'mac_mksound':
  arch/m68k/mac/macboing.c:189: warning: comparison of distinct pointer types lacks a cast
  arch/m68k/mac/macboing.c:211: warning: comparison of distinct pointer types lacks a cast
  arch/m68k/mac/macboing.c: In function 'mac_quadra_start_bell':
  arch/m68k/mac/macboing.c:241: warning: comparison of distinct pointer types lacks a cast
  arch/m68k/mac/macboing.c:263: warning: comparison of distinct pointer types lacks a cast
  arch/m68k/mac/macboing.c: In function 'mac_quadra_ring_bell':
  arch/m68k/mac/macboing.c:283: warning: comparison of distinct pointer types lacks a cast

Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>