Blackfin: cplbinfo: drop d_path() hacks

The cplbinfo was using d_path() to figure out which cpu/cplb was being
parsed.  As Al pointed out, this isn't exactly reliable as it assumes the
static VFS path to be unchanged, and it's just poor form.  So use the
proc_create_data() to properly (and internally) pass the exact cpu/cplb
requested to the parser function.

Reported-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>