ARM: OMAP: fix default sys_ck.rate for boot-time DPLL detection

In the clock init code, the DPLL value set by the bootloader is
queried, but always turns zero due it's parent clock (sys_ck) having
no default rate.  This results in the improper setting of the default
PRCM rate-table entry and any queries of virt_prcm_set rate to return 0.

Following the example of the TI kernel, set the default sys_ck rate to
13MHz.  Could then be overridden in board setup code.
Signed-off-by: Kevin Hilman <khilman@mvista.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>

arch/arm/mach-omap2/clock24xx.h

@@ -581,6 +581,7 @@ static struct clk osc_ck = {		/* (*12, *13, 19.2, *26, 38.4)MHz */
 /* With out modem likely 12MHz, with modem likely 13MHz */
 static struct clk sys_ck = {		/* (*12, *13, 19.2, 26, 38.4)MHz */
 	.name		= "sys_ck",		/* ~ ref_clk also */
+	.rate           = 13000000,
 	.parent		= &osc_ck,
 	.flags		= CLOCK_IN_OMAP242X | CLOCK_IN_OMAP243X |
 				ALWAYS_ENABLED | RATE_PROPAGATES,