mb/hp/snb_ivb_laptops: Remove undefined variable in cmos.default

There is no "volume" defined in cmos.layout now, so removing "volume="
from cmos.default, otherwise building will fail with
CONFIG_USE_OPTION_TABLE set.

Change-Id: I1d6bb68fb927882ddcc052b432bb34b42c58eac7
Signed-off-by: Bill XIE <persmule@hardenedlinux.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/51670
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Iru Cai (vimacs) <mytbk920423@gmail.com>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

src/mainboard/hp/snb_ivb_laptops/cmos.default

@@ -2,5 +2,4 @@ boot_option=Fallback
 debug_level=Debug
 power_on_after_fail=Disable
 nmi=Enable
-volume=0x3
 sata_mode=AHCI