efi: cper: check section header more appropriately

When checking a generic status block, we iterate over all the generic data
blocks. The loop condition checks that the generic data block is valid.
Because the size of data blocks (excluding error data) may vary depending
on the revision and the revision is contained within the data block, we
should ensure that enough of the current data block is valid appropriately
for different revision.

Signed-off-by: Shuai Xue <xueshuai@linux.alibaba.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>