random: vDSO: add missing c-getrandom-y in Makefile

Same as for the gettimeofday CVDSO implementation, add c-getrandom-y to
ease the inclusion of lib/vdso/getrandom.c in architectures' VDSO
builds.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

lib/vdso/Makefile

@@ -4,6 +4,7 @@ GENERIC_VDSO_MK_PATH := $(abspath $(lastword $(MAKEFILE_LIST)))
 GENERIC_VDSO_DIR := $(dir $(GENERIC_VDSO_MK_PATH))
 
 c-gettimeofday-$(CONFIG_GENERIC_GETTIMEOFDAY) := $(addprefix $(GENERIC_VDSO_DIR), gettimeofday.c)
+c-getrandom-$(CONFIG_VDSO_GETRANDOM) := $(addprefix $(GENERIC_VDSO_DIR), getrandom.c)
 
 # This cmd checks that the vdso library does not contain dynamic relocations.
 # It has to be called after the linking of the vdso library and requires it