iPod Classic: fix s5l8702 cache line length.

Use 32 bytes for cache line length (arm926ej-s), this prevents
misalignments of ATA storage buffer which in some builds could
cause weird faults.

Change-Id: I88dc595d251315620ec49b0251ddc039ff47181e
Reviewed-on: http://gerrit.rockbox.org/1031
Reviewed-by: Marcin Bukat <marcin.bukat@gmail.com>