power_supply: bump EC version check that we refuse to run with in olpc_battery

Refuse to run with an EC < 0x44.  We're playing it safe, and this is a pretty
old EC version.

Also, add a comment about why we're checking the EC version.

Signed-off-by: Andres Salomon <dilinger@debian.org>
Cc: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Anton Vorontsov <cbouatmailru@gmail.com>