Makefile: use ' ', not non-existing $(wspfx_SQ)

Change the use of a non-existing variable added in my
0b6d0bc924 (Makefiles: add and use wildcard "mkdir -p" template,
2022-03-03) to use the hardcoded whitespace padding for "QUIET" rules
instead. The wspfx_SQ was left from an earlier (rebased out) commit
preceding 0b6d0bc9246[1].

1. https://lore.kernel.org/git/patch-v4-8.9-3733b0c8df1-20220302T124320Z-avarab@gmail.com/

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

shared.mak

@@ -53,7 +53,7 @@ ifndef V
 	QUIET          = @
 	QUIET_GEN      = @echo '   ' GEN $@;
 
-	QUIET_MKDIR_P_PARENT  = @echo $(wspfx_SQ) MKDIR -p $(@D);
+	QUIET_MKDIR_P_PARENT  = @echo '   ' MKDIR -p $(@D);
 
 ## Used in "Makefile"
 	QUIET_CC       = @echo '   ' CC $@;