fs: smb: common: add missing MODULE_DESCRIPTION() macros

Fix the 'make W=1' warnings:
WARNING: modpost: missing MODULE_DESCRIPTION() in fs/smb/common/cifs_arc4.o
WARNING: modpost: missing MODULE_DESCRIPTION() in fs/smb/common/cifs_md4.o

Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Signed-off-by: Steve French <stfrench@microsoft.com>