ramips: RT1800: fix invalid octal number error

This commit removes the padded zeros in the date formatting.
The padded zeros from the date command causes the numbers
to be interpreted as an octal number by printf. Months, days,
and years with the number 08 or 09 raise an error in printf as an
"invalid octal number" and get interpreted as a zero.

Signed-off-by: Max Qian <public@maxqia.com>
(cherry picked from commit 794349a28a)

target/linux/ramips/image/mt7621.mk

@@ -88,7 +88,7 @@ define Build/belkin-header
 
 	( \
 		type_fw_date=$$(printf "01%02x%02x%02x" \
-			$$(date -d "@$(SOURCE_DATE_EPOCH)" "+%y %m %d")); \
+			$$(date -d "@$(SOURCE_DATE_EPOCH)" "+%-y %-m %-d")); \
 		hw_fw_ver=$$(printf "%02x%02x%02x%02x" \
 			$(hw_ver) $$(echo $(fw_ver) | cut -d. -f-3 | tr . ' ')); \
 		fw_len_crc=$$(gzip -c $@ | tail -c 8 | od -An -tx8 | tr -d ' \n'); \