mtd: spi-nor: make implicit <linux/bitops.h> dependency explicit

We use BIT() in the header. No real problem for now, but it's better to
be accurate.
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

include/linux/mtd/spi-nor.h

@@ -10,6 +10,8 @@
 #ifndef __LINUX_MTD_SPI_NOR_H
 #define __LINUX_MTD_SPI_NOR_H
 
+#include <linux/bitops.h>
+
 /*
  * Note on opcode nomenclature: some opcodes have a format like
  * SPINOR_OP_FUNCTION{4,}_x_y_z. The numbers x, y, and z stand for the number