efi_selftest: compiler flags for dtbdump.o

Fix a typo. Apply the correct compiler flags to dtbdump.o.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/lib/efi_selftest/Makefile b/lib/efi_selftest/Makefile
index 7d6ea30..b02fd56 100644
--- a/lib/efi_selftest/Makefile
+++ b/lib/efi_selftest/Makefile
@@ -8,7 +8,7 @@
 asflags-y += -DHOST_ARCH="$(HOST_ARCH)"
 ccflags-y += -DHOST_ARCH="$(HOST_ARCH)"
 
-CFLAGS_dtbdump_exit.o := $(CFLAGS_EFI) -Os -ffreestanding
+CFLAGS_dtbdump.o := $(CFLAGS_EFI) -Os -ffreestanding
 CFLAGS_REMOVE_dtbdump.o := $(CFLAGS_NON_EFI)
 CFLAGS_efi_selftest_miniapp_exit.o := $(CFLAGS_EFI) -Os -ffreestanding
 CFLAGS_REMOVE_efi_selftest_miniapp_exit.o := $(CFLAGS_NON_EFI)