OMAP: timers: Fix clock source names for OMAP4

The clock sources for timers on OMAP4 (system clock and 32k
clock) have their names wronly populated.
This patch fixes them so the omap_dm_timer_set_source
does not fail anymore.

Signed-off-by: Rajendra Nayak <rnayak@ti.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>