acpi: update comment referencing ACPI ID

ACPI ID for coreboot is now "BOOT" according to CL:18521.

BUG=none
BRANCH=master
TEST=none

Change-Id: I802ce284001b186f6cd8839b8c303d49f42b4d38
Signed-off-by: Joel Kitching <kitching@google.com>
Reviewed-on: https://review.coreboot.org/25042
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/arch/x86/acpigen.c

@@ -223,7 +223,7 @@ void acpigen_write_string(const char *string)
 
 void acpigen_write_coreboot_hid(enum coreboot_acpi_ids id)
 {
-	char hid[9]; /* CORExxxx */
+	char hid[9]; /* BOOTxxxx */
 
 	snprintf(hid, sizeof(hid), "%.4s%04X", COREBOOT_ACPI_ID, id);
 	acpigen_write_name_string("_HID", hid);