[ARM] pxa: fix clock lookup to find specific device clocks

Ensure that the clock lookup always finds an entry for a specific
device and ID before it falls back to finding just by ID.  This
fixes a problem reported by Holger Schurig where the BTUART was
assigned the wrong clock.

Tested-by: Holger Schurig <hs4233@mail.mn-solutions.de>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>