ARM: OMAP3: PM: cpuidle: default to C1 in next_valid_state

If the next state is no found in the next_valid_state function,
fallback to the default value of C1 (which is state 0).
This prevents the use of a bogus state -1 in the rest of the cpuidle
code.

Signed-off-by: Jean Pihet <j-pihet@ti.com>
Signed-off-by: Kevin Hilman <khilman@ti.com>