audit: fix undefined behavior in bit shift for AUDIT_BIT

Shifting signed 32-bit value by 31 bits is undefined, so changing
significant bit to unsigned. The UBSAN warning calltrace like below:

UBSAN: shift-out-of-bounds in kernel/auditfilter.c:179:23
left shift of 1 by 31 places cannot be represented in type 'int'
Call Trace:
 <TASK>
 dump_stack_lvl+0x7d/0xa5
 dump_stack+0x15/0x1b
 ubsan_epilogue+0xe/0x4e
 __ubsan_handle_shift_out_of_bounds+0x1e7/0x20c
 audit_register_class+0x9d/0x137
 audit_classes_init+0x4d/0xb8
 do_one_initcall+0x76/0x430
 kernel_init_freeable+0x3b3/0x422
 kernel_init+0x24/0x1e0
 ret_from_fork+0x1f/0x30
 </TASK>

Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
[PM: remove bad 'Fixes' tag as issue predates git, added in v2.6.6-rc1]
Signed-off-by: Paul Moore <paul@paul-moore.com>