drm/amdgpu: Unlock bo_list_mutex after error handling

Get below kernel WARNING backtrace when pressing ctrl-C to kill kfdtest
application.

If amdgpu_cs_parser_bos returns error after taking bo_list_mutex, as
caller amdgpu_cs_ioctl will not unlock bo_list_mutex, this generates the
kernel WARNING.

Add unlock bo_list_mutex after amdgpu_cs_parser_bos error handling to
cleanup bo_list userptr bo.

 WARNING: kfdtest/2930 still has locks held!
 1 lock held by kfdtest/2930:
  (&list->bo_list_mutex){+.+.}-{3:3}, at: amdgpu_cs_ioctl+0xce5/0x1f10 [amdgpu]
  stack backtrace:
   dump_stack_lvl+0x44/0x57
   get_signal+0x79f/0xd00
   arch_do_signal_or_restart+0x36/0x7b0
   exit_to_user_mode_prepare+0xfd/0x1b0
   syscall_exit_to_user_mode+0x19/0x40
   do_syscall_64+0x40/0x80
Signed-off-by: Philip Yang <Philip.Yang@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c

@@ -992,6 +992,7 @@ static int amdgpu_cs_parser_bos(struct amdgpu_cs_parser *p,
 		kvfree(e->user_pages);
 		e->user_pages = NULL;
 	}
+	mutex_unlock(&p->bo_list->bo_list_mutex);
 	return r;
 }