cifsd: fix boolreturn.cocci warnings

fs/cifsd/smb2pdu.c:8098:8-9: WARNING: return of 0/1 in function
'smb2_is_sign_req' with return type bool

 Return statements in functions returning bool should use  true/false
instead of 1/0.
Generated by: scripts/coccinelle/misc/boolreturn.cocci

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: kernel test robot <lkp@intel.com>
Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Steve French <stfrench@microsoft.com>