ARM: OMAP5: PRM: Fix reboot handling

Use the correct register offset for issuing the
reset command in OMAP5. Since dev_inst is set dynamically
OMAP4 should not be affected by this change.

Signed-off-by: Vaibhav Bedia <vaibhav.bedia@gmail.com>
Tested-by: Lokesh Vutla <lokeshvutla@ti.com>
Acked-by: Rajendra Nayak <rnayak@ti.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>