vboot_reference: update VbGetSystemPropertyString api
`VbGetSystemPropertyString` header promises that the property string
will be read into the passed in dest buffer, however for some system
properties the values are not placed in buffer but returned directly.
this patch fixes that error
Output calling properties
```
Property Name: hwid Buf: REDRIX-CLQY C4B-D5K-D3D-W7F-324-Y6H Ret: 0
Property Name: kernkey_vfy Buf: sig Ret: 0
Property Name: mainfw_act Buf: recovery Ret: 0
Property Name: vdat_lfdebug Buf: Check A result=0
Check B result=0
Firmware index booted=0xff
TPM combined version at start=0x00010001
Lowest combined version from firmware=0x00000000
Ret: 0
Property Name: fw_try_next Buf: A Ret: 0
Property Name: fw_tried Buf: A Ret: 0
Property Name: fw_result Buf: success Ret: 0
Property Name: fw_prev_tried Buf: A Ret: 0
Property Name: fw_prev_result Buf: unknown Ret: 0
Property Name: dev_default_boot Buf: disk Ret: 0
Property Name: minios_priority Buf: A Ret: 0
get property with null minios_priority failed
get property with 0 size minios_priority failed
```
BRANCH=none
BUG=b:279629907
TEST=Tested with an executable on brya
TEST=Compared `crossytem` output with and without change.
Signed-off-by: Saketh Pothireddy <spothire@chromium.org>
Cq-Depend: 4520625, 4521035
Change-Id: I5640f1ff301a4581519c9764965afa838ff40809
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/4517774
Reviewed-by: Julius Werner <jwerner@chromium.org>
Tested-by: Saketh Pothireddy <spothire@google.com>
Commit-Queue: Saketh Pothireddy <spothire@google.com>
6 files changed
