read() might return less than $count bytes which is only an upper limit.
The user is supposed to repeat the command to fill a buffer completely.
So use the convenience wrapper read_full in memcmp.
This fixes memcmp on /dev/nand0 on an Armada XP.
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>