soc/amd/stoneyridge: Correct ACPI CPU string prefix

Commit 9550e97 [acpi: correct the processor devices scope] changed
the default CPU scope from _PR to _SB, but the default prefix in
Stoneyridge's Kconfig was missed, leading to ACPI errors for
'AE_NOT_FOUND for object \_PR.P00n.' Fix the default prefix and
eliminate the errors reported in dmesg.

Test: boot Linux w/5.3 kernel on google/liara, check for errors

Change-Id: I5611b6836062a0a9f90036d7fe40cd98bd730af3
Signed-off-by: Matt DeVillier <matt.devillier@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/42627
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
diff --git a/src/soc/amd/stoneyridge/Kconfig b/src/soc/amd/stoneyridge/Kconfig
index 9bb5604..f093e28 100644
--- a/src/soc/amd/stoneyridge/Kconfig
+++ b/src/soc/amd/stoneyridge/Kconfig
@@ -296,7 +296,7 @@
 
 config ACPI_CPU_STRING
 	string
-	default "\\_PR.P%03d"
+	default "\\_SB.P%03d"
 
 config ACPI_BERT
 	bool "Build ACPI BERT Table"