fs/fat: Avoid corruption of sectors following the FAT

The FAT is read/flushed in segments of 6 (FATBUFBLOCKS) disk sectors. The
last segment may be less than 6 sectors, cap the length.

Signed-off-by: Stefan Brüns <stefan.bruens@rwth-aachen.de>
Reviewed-by: Benoît Thébaudeau <benoit.thebaudeau.dev@gmail.com>
diff --git a/fs/fat/fat.c b/fs/fat/fat.c
index df9f2b5..6319581 100644
--- a/fs/fat/fat.c
+++ b/fs/fat/fat.c
@@ -202,6 +202,7 @@
 		__u32 fatlength = mydata->fatlength;
 		__u32 startblock = bufnum * FATBUFBLOCKS;
 
+		/* Cap length if fatlength is not a multiple of FATBUFBLOCKS */
 		if (startblock + getsize > fatlength)
 			getsize = fatlength - startblock;