ahci: Fix cache align error messages

Align the ATA ID buffer to the cache-line boundary. This gets rid
of the below error mesages on ARM v7 platforms.

 scanning bus for devices...
 ERROR: v7_dcache_inval_range - start address is not aligned - 0xfee48618
 ERROR: v7_dcache_inval_range - stop address is not aligned - 0xfee48818

CC: Aneesh V <aneesh@ti.com>
Signed-off-by: Roger Quadros <rogerq@ti.com>