arm host: Fix linker warning (m68k targets)

Compilation of m68k-softmmu or m68k-linux-user on arm host
(or cross compilation for arm) results in a linker warning:

  LINK  m68k-softmmu/qemu-system-m68k
m68k-dis.o: warning: definition of `floatformat_ieee_single_little' overriding common
arm-dis.o: warning: common is here
/usr/lib/gcc/arm-linux-gnueabi/4.3.2/../../../../arm-linux-gnueabi/bin/ld: Warning: size of symbol `floatformat_ieee_single_little' changed from 4 in arm-dis.o to 48 in m68k-dis.o

floatformat_ieee_single_little is declared in arm-dis.c and m68k-dis.c,
and both declarations don't match, so this is an error.

The symbol is not needed in arm-dis.c, so I removed it there.

Signed-off-by: Stefan Weil <weil@mail.berlios.de>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>