scsi: avoid an off-by-one error in megasas_mmio_write

While reading magic sequence(MFI_SEQ) in megasas_mmio_write,
an off-by-one error could occur as 's->adp_reset' index is not
reset after reading the last sequence.

Reported-by: YY Z <bigbird475958471@gmail.com>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
Message-Id: <20170424120634.12268-1-ppandit@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>