uboot-envtools: adjust compile patch to version v2021.01

with u-boot v2020.07 some variables have been renamed so this patch needs to be adjusted
otherwise at least with macOS as build system there are build errors

Signed-off-by: Ronny Kotzschmar <[email protected]>

package/boot/uboot-envtools/patches/001-compile.patch

@@ -5,10 +5,10 @@
  override HOSTCC = $(CC)
  
 +ifneq ($(TARGET_CFLAGS),)
-+HOSTCFLAGS = $(TARGET_CFLAGS)
++KBUILD_HOSTCFLAGS = $(TARGET_CFLAGS)
 +endif
 +ifneq ($(TARGET_LDFLAGS),)
-+HOSTLDFLAGS = $(TARGET_LDFLAGS)
++KBUILD_HOSTLDFLAGS = $(TARGET_LDFLAGS)
 +endif
 +
  # Compile for a hosted environment on the target