ARM: 6967/1: ep93xx: ts72xx: fix board model detection

Fix the obvious error in board detection logic, because according to the TS's
manual, the model is stored in the least three significant bits. For example
the byte read on my ts-7300 is 0x23 and the detection then fails.

Cc: Ryan Mallon <ryan@bluewatersys.com>
Acked-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Petr Štetiar <ynezz@true.cz>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>