mtd: spi-nor: fix stm_is_locked_sr() parameters

stm_is_locked_sr() takes the status register (SR) value as the last
parameter, not the second.

Reported-by: Bayi Cheng <bayi.cheng@mediatek.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Cc: Bayi Cheng <bayi.cheng@mediatek.com>