It has to be "its" because it's a possessive pronoun meaning "belonging to it" just as "his" means "belonging to him" and "your" means "belonging to you". So by virtue of being a possessive pronoun, "its" already denotes ownership without need to add (incorrectly) an apostrophe and, thus, change its meaning to "it is" or "it has".

"It's going to lose its loose nut", is a useful phrase to remember. :-)

(How could "its" ever be mistaken for a plural? Do you think "his" is the plural of "hi"?) lol