ARM: OMAP2+: CM: cm_inst offset s16->u16

Most of the AM43x CM reg address offsets are with MSB bit '1' (on
16-bit value) leading to arithmetic miscalculations while calculating
CLOCK ENABLE register's address because cm_inst field was a type of
"const s16", so make it "const u16".

Also modify relevant functions so as to take care of the above.

[afzal@ti.com: fixup and cleanup]

Signed-off-by: Ankur Kishore <a-kishore@ti.com>
Signed-off-by: Afzal Mohammed <afzal@ti.com>
Acked-by: Rajendra Nayak <rnayak@ti.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>