libata: remove ATA_FLAG_MMIO

Commit 0d5ff566779f894ca9937231a181eb31e4adff0e (libata: convert to iomap)
removed all checks of ATA_FLAG_MMIO but neglected to remove the flag itself.
Do it now, at last...

Signed-off-by: Sergei Shtylyov <[email protected]>
Signed-off-by: Jeff Garzik <[email protected]>
29 files changed