fix(stm32mp1): correct dtc version check

Depending on the shell used, the grep command can fail, leading to
a wrong dtc version detection. Correct that by adding quotes.

Signed-off-by: Yann Gautier <yann.gautier@foss.st.com>
Change-Id: I329ec929559c94bf1bf99b127662c9d978e067cf

plat/st/stm32mp1/platform.mk

@@ -109,7 +109,7 @@ endif
 endif
 
 $(eval DTC_V = $(shell $(DTC) -v | awk '{print $$NF}'))
-$(eval DTC_VERSION = $(shell printf "%d" $(shell echo ${DTC_V} | cut -d- -f1 | sed "s/\./0/g" | grep -o [0-9]*)))
+$(eval DTC_VERSION = $(shell printf "%d" $(shell echo ${DTC_V} | cut -d- -f1 | sed "s/\./0/g" | grep -o "[0-9]*")))
 DTC_CPPFLAGS		+=	${INCLUDES}
 DTC_FLAGS		+=	-Wno-unit_address_vs_reg
 ifeq ($(shell test $(DTC_VERSION) -ge 10601; echo $$?),0)