Remove assert on exec_bfd in cris_delayed_get_disassembler

cris_delayed_get_disassembler has an assert that exec_bfd can't be
NULL, but this assert can be triggered like this,

(gdb) set architecture cris
The target architecture is assumed to be cris
(gdb) disassemble 0x0,+4
Dump of assembler code from 0x0 to 0x4:
   0x00000000:
../../binutils-gdb/gdb/cris-tdep.c:3798: internal-error: int cris_delayed_get_disassembler(bfd_vma, disassemble_info*): Assertion `exec_bfd != NULL' failed.
A problem internal to GDB has been detected,
further debugging may prove unreliable.

however, cris_get_disassembler does have code to handle the case that
bfd is NULL,

  /* If there's no bfd in sight, we return what is valid as input in all
     contexts if fed back to the assembler: disassembly *with* register
     prefix.  Unfortunately this will be totally wrong for v32.  */
  if (abfd == NULL)
    return print_insn_cris_with_register_prefix;

This patch is to remove this assert.

gdb:

2016-12-12  Yao Qi  <yao.qi@linaro.org>

	PR tdep/20955
	* cris-tdep.c (cris_delayed_get_disassembler): Remove the
	assert.

gdb/ChangeLog

@@ -1,3 +1,9 @@
+2016-12-12  Yao Qi  <yao.qi@linaro.org>
+
+	PR tdep/20955
+	* cris-tdep.c (cris_delayed_get_disassembler): Remove the
+	assert.
+
 2016-12-09  Pedro Alves  <palves@redhat.com>
 
 	* Makefile.in (ALL_TARGET_OBS): Remove vax-obsd-tdep.o.

gdb/cris-tdep.c

@@ -3792,10 +3792,7 @@ static int
 cris_delayed_get_disassembler (bfd_vma addr, struct disassemble_info *info)
 {
   int (*print_insn) (bfd_vma addr, struct disassemble_info *info);
-  /* FIXME: cagney/2003-08-27: It should be possible to select a CRIS
-     disassembler, even when there is no BFD.  Does something like
-     "gdb; target remote; disassmeble *0x123" work?  */
-  gdb_assert (exec_bfd != NULL);
+
   print_insn = cris_get_disassembler (exec_bfd);
   gdb_assert (print_insn != NULL);
   return print_insn (addr, info);