[ARM] 4829/1: add .get method to pxa-cpufreq to silence a warning

The .get method is needed for suspend/resume. Otherwise you
get this in dmesg:

cpufreq: suspend failed to assert current frequency is what timing core thinks it is.
cpufreq: resume failed to assert current frequency is what timing core thinks it is.

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