fritz-tools: fix returning wrong values due to strncmp usage

fritz-tools: fix returning wrong values due to strncmp usage

When having two keys that start with the same characters and the second
key just has one character more nand_tffs_read and tffs_read return the
wrong value for the longer key. This is due to the usage of strncmp in
combination with the length of the shorter key which is usually first in
the list before the longer key and when strncmp matches, the search is
stopped. The problem only occurs when the length of the two keys is
different, not if just the last character is different. The fix is to
use strcmp and as such it will only return the value if the key (name)
and the key to look for (namefilter) have the same value and length. A
sample case returning wrong values is when keys macwlan and macwlan2 are
defined and querying macwlan2 returns the value for macwlan.

Signed-off-by: Daniel Kestrel <kestrel1974@t-online.de>