src/ext4_resize.c: Refactor code and ensure accurate errno is returned

src/ext4_resize.c: Refactor code and ensure accurate errno is returned

The current implementation of ext4_resize returned 1 whenever
there was an error. Modify this to return the correct error code.
This is important for tests that rely on correct error reporting, by
the kernel, for ext4 resize functionality.

Additionaly, perform some code cleanup.

Signed-off-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Reviewed-by: Ritesh Harjani <riteshh@linux.ibm.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>