efi/Makefile: remove effective double "//"

During the string substitution, an addtional '/' is added unnecessarily.

Signed-off-by: Gene Cumm <gene.cumm@gmail.com>
diff --git a/efi/Makefile b/efi/Makefile
index bbf23f2..d3788d9 100644
--- a/efi/Makefile
+++ b/efi/Makefile
@@ -18,17 +18,17 @@
 CFLAGS += -Wno-strict-prototypes
 
 CORE_CSRC := $(wildcard $(core)/*.c $(core)/*/*.c $(core)/*/*/*.c)
-CORE_COBJ := $(subst $(core),$(OBJ)/../core/,$(patsubst %.c,%.o,$(CORE_CSRC)))
+CORE_COBJ := $(subst $(core),$(OBJ)/../core,$(patsubst %.c,%.o,$(CORE_CSRC)))
 
 # We don't want to include any of the networking stack or the thread
 # code since it will be implemented completely differently for EFI.
-FILTERED_OBJS:= $(subst $(core),$(OBJ)/../core/,$(patsubst %.c,%.o, \
+FILTERED_OBJS:= $(subst $(core),$(OBJ)/../core,$(patsubst %.c,%.o, \
 	$(wildcard $(core)/legacynet/*.c) \
 	$(wildcard $(core)/fs/pxe/*.c) \
 	$(wildcard $(core)/thread/*.c)))
 
 # Don't include unit tests
-FILTERED_OBJS += $(subst $(core),$(OBJ)/../core/, \
+FILTERED_OBJS += $(subst $(core),$(OBJ)/../core, \
 	$(patsubst %.c,%.o,$(shell find $(core) -path "*/tests/*.c" -print)))
 
 # Don't include console objects