OMAP3 clock: use pr_debug() rather than pr_info() in some clock change code

The CORE DPLL M2 frequency change code should use pr_debug(), not
pr_info(), for its debug messages.  Same with
omap2_clksel_round_rate_div().  While here, convert a few printk(KERN_ERR ..
into pr_err().

Signed-off-by: Paul Walmsley <paul@pwsan.com>