cifs: print warning when conflicting soft vs. hard mount options specified

If the user specifies conflicting hard vs. soft mount options
(or nosoft vs. nohard) print a warning to dmesg

We were missing a warning when a user e.g. mounted with both
"hard,soft" mount options.

Reviewed-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Signed-off-by: Steve French <stfrench@microsoft.com>