ARM: OMAP2+: timer: initialize before using oh_name

of_property_read_string_index(...,&oh_name) in omap_dm_timer_init_one
does not alter the value of 'oh_name' even if the relevant function
fails and as 'oh_name' in stack may have a non-zero value, it would
be misunderstood by timer code that DT has specified "ti,hwmod"
property for timer. 'oh_name' in this scenario would be a junk value,
this would result in module not being enabled by hwmod API's for
timer, and in turn crash.

Signed-off-by: Afzal Mohammed <afzal@ti.com>
Acked-by: Jon Hunter <jgchunter@gmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>