usb: gadget/function/f_fs string table fix for multiple languages

Fixes bug with the handling of more than one language in
the string table in f_fs.c.
str_count was not reset for subsequent language codes.
str_count-- "rolls under" and processes u32 max strings on
the processing of the second language entry.
The existing bug can be reproduced by adding a second language table
to the structure "strings" in tools/usb/ffs-test.c.
Signed-off-by: Dean Anderson <dean@sensoray.com>
Link: https://lore.kernel.org/r/20210317224109.21534-1-dean@sensoray.com
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/gadget/function/f_fs.c

@@ -2640,6 +2640,7 @@ static int __ffs_data_got_strings(struct ffs_data *ffs,
 
 	do { /* lang_count > 0 so we can use do-while */
 		unsigned needed = needed_count;
+		u32 str_per_lang = str_count;
 
 		if (len < 3)
 			goto error_free;
@@ -2675,7 +2676,7 @@ static int __ffs_data_got_strings(struct ffs_data *ffs,
 
 			data += length + 1;
 			len -= length + 1;
-		} while (--str_count);
+		} while (--str_per_lang);
 
 		s->id = 0;   /* terminator */
 		s->s = NULL;