QC common: fix compiler complaint, missing <string.h>

Change-Id: I5b5b7bc61dd82fb1b866857d60926b057fae3715
Signed-off-by: T Michael Turney <mturney@codeaurora.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/33445
Reviewed-by: HAOUAS Elyes <ehaouas@noos.fr>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/soc/qualcomm/common/qclib.c

@@ -16,6 +16,7 @@
 #include <console/cbmem_console.h>
 #include <cbmem.h>
 #include <boardid.h>
+#include <string.h>
 #include <fmap.h>
 #include <assert.h>
 #include <arch/mmu.h>