cpufreq: OMAP: Handle missing frequency table on SMP systems

On OMAP4, if the first CPU fails to get a valid frequency table (this
could happen if the platform does not register any OPP table), the
subsequent CPU instances end up dealing with a NULL freq_table and
crash.

Check for an already existing freq_table, before trying to create one,
and increment the freq_table_users only if the table is sucessfully
created.

Signed-off-by: Rajendra Nayak <rnayak@ti.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Cc: <linux-pm@vger.kernel.org>
Signed-off-by: Kevin Hilman <khilman@ti.com>