mtd: nand: fix off-by-one read retry mode counting

A flash may support N read retry voltage threshold modes, numbered 0
through N-1 (where mode 0 represents the initial state). However,
nand_do_read_ops() tries to use mode 0 through N.

This off-by-one error shows up, for instance, when using nanddump, and
we have cycled through available modes:

    nand: setting READ RETRY mode 0
    nand: setting READ RETRY mode 1
    nand: setting READ RETRY mode 2
    nand: setting READ RETRY mode 3
    nand: setting READ RETRY mode 4
    nand: setting READ RETRY mode 5
    nand: setting READ RETRY mode 6
    nand: setting READ RETRY mode 7
    nand: setting READ RETRY mode 8
    libmtd: error!: cannot read 8192 bytes from mtd0 (eraseblock 20, offset 0)
            error 22 (Invalid argument)
    nanddump: error!: mtd_read

Tested on Micron MT29F64G08CBCBBH1, with 8 retry modes.
Signed-off-by: NBrian Norris <computersforpeace@gmail.com>
Acked-by: NHuang Shijie <b32955@freescale.com>

drivers/mtd/nand/nand_base.c

@@ -1584,7 +1584,7 @@ static int nand_do_read_ops(struct mtd_info *mtd, loff_t from,
 			}
 
 			if (mtd->ecc_stats.failed - ecc_failures) {
-				if (retry_mode + 1 <= chip->read_retries) {
+				if (retry_mode + 1 < chip->read_retries) {
 					retry_mode++;
 					ret = nand_setup_read_retry(mtd,
 							retry_mode);