omap: fix fncpy API call

Fix a potential problem with function types when calling the
fncpy API to copy the PM code functions to SRAM.

Signed-off-by: Jean Pihet <j-pihet@ti.com>
Reviewed-by: Dave Martin <dave.martin@linaro.org>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>