fs: fat: fix set_cluster()

Avoid CoverityScan warning SIGN_EXTENSION by changing the type of
parameter size of set_cluster().

Avoid leaking stack content when writing an incomplete last sector.

Reported-by: Coverity (CID: 184096)
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
1 file changed