OMAP2xxx clock: clk2xxx.c doesn't compile if CPUFREQ is enabled

if we enable CPUFREQ we can't build omap2 for two reasons,
one of them is fixed by the patch below.

It's failing because the __must_be_array() check in
ARRAY_SIZE() is failing and printing the following message:

arch/arm/mach-omap2/clock2xxx.c:453: error: negative width in bit-field '<anonymous>'

Signed-off-by: Felipe Balbi <felipe.balbi@nokia.com>
[paul@pwsan.com: commit message updated; changed rate variable name]
Signed-off-by: Paul Walmsley <paul@pwsan.com>