OMAP3630: PM: don't warn the user with a trace in case of PM34XX_ERRATUM

In case in user has a OMAP3630 < ES1.2 the kernel should warn the user
about the ERRATUM, but using pr_warn instead of WARN_ON is already
enough, as there is nothing else the user can do besides changing the
board.

Signed-off-by: Ricardo Salveti de Araujo <ricardo.salveti@canonical.com>
Signed-off-by: Kevin Hilman <khilman@ti.com>