Makefile: fix suspicious line

Emacs (the good and infalible text editor) detects a suspicious line in
Makefile, this line contains both space and tab (something that could be
introduced by a less sophisticated text editor) that is not correct
for a Makefile.

fixes #2286

Signed-off-by: Julio Montes <julio.montes@intel.com>

Makefile

@@ -243,7 +243,7 @@ endif
 ifneq (,$(QEMUVIRTIOFSCMD))
 	KNOWN_HYPERVISORS += $(HYPERVISOR_QEMU_VIRTIOFS)
 
- 	CONFIG_FILE_QEMU_VIRTIOFS = configuration-qemu-virtiofs.toml
+	CONFIG_FILE_QEMU_VIRTIOFS = configuration-qemu-virtiofs.toml
 	CONFIG_QEMU_VIRTIOFS = $(CLI_DIR)/config/$(CONFIG_FILE_QEMU_VIRTIOFS)
 	CONFIG_QEMU_VIRTIOFS_IN = $(CONFIG_QEMU_VIRTIOFS).in