tools: binman: ti_board_cfg: Fix pylint error over 'br'

With a newer pylint, we get a warning that 'br' could be used before
assignment. Fix this by declaring br first as an empty bytearray.

Reviewed-by: Neha Malcom Francis <n-francis@ti.com>
Signed-off-by: Tom Rini <trini@konsulko.com>

tools/binman/etype/ti_board_config.py

@@ -119,6 +119,7 @@ class Entry_ti_board_config(Entry_section):
             array of bytes representing value
         """
         size = 0
+        br = bytearray()
         if (data_type == '#/definitions/u8'):
             size = 1
         elif (data_type == '#/definitions/u16'):