We read the ROM version to determine the CPU revision before B1 chip.
The rom version is 4 bytes word, it has major version at low byte,
minor version at second byte.

On B0.1 chip, the value is 0x1020 not 0x20, if reading the word and comparing
with 0x20, the result is wrong.

Fix the issue by only reading the lowest byte for major version.

Signed-off-by: Ye Li <ye.li@nxp.com>
(cherry picked from commit 8d0812e63155cca91ecb78c630a450e7d5e5fd00)