hw/block/pflash_cfi02: Fix reset command not ignored during erase

hw/block/pflash_cfi02: Fix reset command not ignored during erase

When the flash device is performing a chip erase, all commands are
ignored. When it is performing a sector erase, only the erase suspend
command is valid, which is currently not supported.

In particular, the reset command should not cause the device to reset to
read array mode while programming is on going.

Signed-off-by: Stephen Checkoway <stephen.checkoway@oberlin.edu>
Message-Id: <20190426162624.55977-8-stephen.checkoway@oberlin.edu>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>