If the partition size is too small for imx_bbu_nand_update(),
this can lead to an infinite loop in the imx_bbu_firmware_fcb_start_page()
function, because imx_bbu_firmware_max_blocks() returns zero.
Fix this by place imx_bbu_firmware_max_blocks() a bit early.

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>