ext2: trivial indentation fix.

This memset() line was indented with seven spaces, this patch fixes
it to use a tab instead. Yes, very trivial but it's the third time
I have to look at this line..

Signed-off-by: Luiz Capitulino <lcapitulino@mandriva.com.br>
Signed-off-by: Adrian Bunk <bunk@stusta.de>