pstore: remove superfluous memory size check

All previous checks will fail with error if memory size
is not sufficient to register a zone, so this legacy
check has become redundant.

Signed-off-by: Mark Salyzyn <salyzyn@android.com>
Acked-by: Kees Cook <keescook@chromium.org>
Change-Id: Ie21c988ae0b1ebb0dafa6c0c0b069e9cfe1e8506