scsi/esp: Rename the ESP macro to ESP_STATE

SunOS defines ESP (x86 register) in <sys/regset.h> as 7.

This fixes build on SmartOS (Joyent).

Signed-off-by: Kamil Rytarowski <n54@gmx.com>
Message-Id: <20170909142116.26816-1-n54@gmx.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>