OMAP3: id: add fallthrough warning; fix some CodingStyle issues

Emit a warning to the console in omap3_check_revision() if that code
cannot determine what type of SoC the system is currently running on.

Remove some extra whitespace, remove some duplicate code, and
add an appropriate comment to a fallthrough case.

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