m68k: fix sigset_t accessor functions

The sigaddset/sigdelset/sigismember functions that are implemented with
bitfield insn cannot allow the sigset argument to be placed in a data
register since the sigset is wider than 32 bits.  Remove the "d"
constraint from the asm statements.

The effect of the bug is that sending RT signals does not work, the signal
number is truncated modulo 32.

Signed-off-by: Andreas Schwab <schwab@linux-m68k.org>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: stable@vger.kernel.org