drivers/db8500-cpufreq: delete dangling include

There was a dangling #include <mach/id.h> in the cpufreq
file missing from commit
7a4f2609
"ARM: ux500: de-globalize <mach/id.h>"

Causing build regressions when building with cpufreq
support.

Cc: arm@kernel.org
Cc: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>