mtd: st_spi_fsm: Fix [-Wsign-compare] build warning

drivers/mtd/devices/st_spi_fsm.c:1647:17:
  warning: comparison between signed and unsigned integer expressions

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
1 file changed