The mount options matching code was incorrectly testing for string

The mount options matching code was incorrectly testing for string
termination or '=' of m->option[len], where len = strlen(m->option).  Also,
at that particular point in the code the opt[] string has already been
stripped of any '='.  The original code must have been intended to check
an unstripped opt[] string but with opt[] stripped it really just needs to
do a case case-insensitive match.

Noticed-by: Johannes Hofmann <Johannes.Hofmann@gmx.de>