board: ti: am57xx: Prevent init_sata() from being called twice

init_sata() is done as part of scsi_init() in
arch/arm/cpu/armv7/omap-common/sata.c so no need to duplicate
it here.

This seems to fix SATA problems in the kernel when CONFIG_TI_PIPE3 is
configured as loadable module.

Cc: Cooper Jr., Franklin <fcooper@ti.com>
Cc: Nishanth Menon <nm@ti.com>
Signed-off-by: Roger Quadros <rogerq@ti.com>