flasher: Use BMC_MTD to represent bmc

We were using a boolean to say "yep, we're talking to the BMC flash".
Use the enum that is provided by libflash to do this.

Change-Id: If40ac3ee64c0827693c93c64ea18a0a34ef79a46
Signed-off-by: Joel Stanley <joel@jms.id.au>
1 file changed