mtd: gpmi: change the code for clocks

The gpmi nand driver may needs several clocks(MX6Q needs five clocks).

In the old clock framework, all these clocks are chained together,
all you need is to manipulate the first clock.

But the kernel uses the common clk framework now, which forces us to
get the clocks one by one. When we use them, we have to enable them
one by one too.

Signed-off-by: Huang Shijie <shijie8@gmail.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>