I think this entry in Du Cange's Glossarium ad Scriptores Mediae et Infimae Graecitatis is what you want. I find it a bit hard to make out the entire entry, but this excerpt in it seems relevant:
ὄρμος, τὸ μέρος τοῦ λιμένος, εἰς ὃ ἑλκόμεναι αἱ νῆες δέδενται · ὃ οἱ
κοινοὶ σκάλαν λέγουσι.
This describes an ὄρμος (whose meanings include such meanings as "cord", "chain", ... "moorings", "haven", according to L&S) as the part of the harbour where ships are drawn and tied (there are probably better nautical terms for this), and which the common people refer to as a σκάλα.
Here's an image of the entry: (The bit I've quoted above is the first bit of Greek you see in the image below.)
There are a few other points to note here.
First, Du Cange devotes more than one entry to ΣΚΑΛΑ, the first one being devoted to its meanings deriving from κλῖμαξ or ladder, and containing other definitions such as "stirrup". The entry I've provided an image for is a separate entry.
Second, I've included only the first part, which ends at the botton of a page. The definition continues on the next page.
Third, at the very bottom of the image, you will see a quote from "de Bellis Francor.[um] in Morea". This refers to the Chronicle of Morea. I looked up where this line comes from for context, and will quote it below.
This is a passage from the Chronicle of Morea in which σκάλα is used, along with my own tentative translation. (Disclaimer: I am not familiar with the type of Greek used in the Chronicle of Morea, so my translation is quite tentative, and may be full of errors.)
(Tentative translation has been revised due to suggestion by TKR.)
Ὅμως, ὡς ἦτον φρόνιμος, ἐπαρηγορήθη μόνος
κι ὤρθωσεν τὰ φουσσᾶτα του, στὴν Κόρινθον ἀπῆλθεν·
μὲ δύναμιν ἀπέρασε τὴν σκάλαν τῶν Μεγάρων,
μὲ πόλεμον ἐκέρδισεν ἐκείνην τὴν κλεισοῦραν.
Ὁ Μέγας Κύρης τὸ ἔμαθεν κ᾿ ἐθλίβη το μεγάλως,
διατὶ ἔμαθε ὅτι ἐπέρασεν ὁ πρίγκιπας τὴν σκάλαν
κ᾿ ἐσέβην εἰς τὸν τόπον του κ᾿ ὑπάει γυρεύοντά τον.
Nevertheless, as he was wise, he took counsel by himself (?)
and raised up his armies, [and] departed for Corinth.
with power he passed across the σκάλαν of Megara,
with war he gained that strait.
The Great Lord learned of it, and was afflicted greatly,
because he learned that the prince had gotten through the σκάλαν
and entered his place and wandered around it.