OMAP3: id: remove duplicate code for testing SoC ES level

omap3_cpuinfo() contains essentially duplicated code from
omap3_check_revision(), just for the purpose of determining the chip ES level.
Set the cpu_rev char array pointer in omap3_check_revision() instead,
and drop the now-useless code from omap3_cpuinfo().

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Tested-by: Igor Grinberg <grinberg@compulab.co.il>
Tested-by: Abhilash Koyamangalath <abhilash.kv@ti.com>