mmc: core: fix the pointer cast of freq_table

The freq_table in devfreq_dev_profile is changed from
unsigned int to unsigned long. Fix the pointer cast here
by allocating a individual memory to pointer freq_table.

Change-Id: I2f7f17df0c3bd8de725daca1aa89572ce1911edd
Signed-off-by: Xiaonian Wang <xiaonian@codeaurora.org>