Makefile: Fix distclean make target

The default install directory is not being removed correctly by
distclean make target due to recent changes. This patch fixes
distclean make target to fix default install directory removal.

Fixes: 82ae8e8fe2 ("makefile: Do setup of the install target
more flexible")
Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Atish Patra <atish.patra@wdc.com>

Makefile

@@ -29,10 +29,11 @@ endif
 ifeq ($(build_dir),$(CURDIR))
 $(error Build directory is same as source directory.)
 endif
+install_root_dir_default=$(CURDIR)/install
 ifdef I
  install_root_dir=$(shell $(READLINK) -f $(I))
 else
- install_root_dir=$(CURDIR)/install/usr
+ install_root_dir=$(install_root_dir_default)/usr
 endif
 ifeq ($(install_root_dir),$(CURDIR))
 $(error Install root directory is same as source directory.)
@@ -456,7 +457,7 @@ ifeq ($(build_dir),$(CURDIR)/build)
 	$(if $(V), @echo " RM        $(build_dir)")
 	$(CMD_PREFIX)rm -rf $(build_dir)
 endif
-ifeq ($(install_root_dir),$(CURDIR)/install)
-	$(if $(V), @echo " RM        $(install_root_dir)")
-	$(CMD_PREFIX)rm -rf $(install_root_dir)
+ifeq ($(install_root_dir),$(install_root_dir_default)/usr)
+	$(if $(V), @echo " RM        $(install_root_dir_default)")
+	$(CMD_PREFIX)rm -rf $(install_root_dir_default)
 endif