test: undefined reference to 'sscanf'

Compiling with CONFIG_UNIT_TEST=y leads to:

aarch64-linux-gnu-ld.bfd:
test/lib/sscanf.c:50: undefined reference to `sscanf'

Add missing build dependency.

Fixes:e87dfb0526be ("lib: sscanf: add sscanf implementation")
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

test/lib/Makefile

@@ -7,7 +7,7 @@ obj-$(CONFIG_EFI_LOADER) += efi_device_path.o
 obj-$(CONFIG_EFI_SECURE_BOOT) += efi_image_region.o
 obj-y += hexdump.o
 obj-y += lmb.o
-obj-y += sscanf.o
+obj-$(CONFIG_SSCANF) += sscanf.o
 obj-y += string.o
 obj-$(CONFIG_ERRNO_STR) += test_errno_str.o
 obj-$(CONFIG_UT_LIB_ASN1) += asn1.o