ata: ahci_brcm: Match BCM63138 compatible strings

Match the "brcm,bcm63138-ahci" compatible string in order to allow this
driver to probe on such platforms.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>