fs:ext4:fix: Code refactoring to suppress compiler warnings

Several fixes to suppress compiler's (eldk-5.[12].x  gcc 4.6)
warning  [-Wunused-but-set-variable]

Signed-off-by: Lukasz Majewski <l.majewski@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>