nand: Correct NAND erase percentage output

For NAND erase sizes smaller than one NAND erase block, erase
percentage output becomes grater than 100% e.g.

-- cut --
  > nand info
Device 0: NAND 64MiB 1,8V 8-bit, sector size 16 KiB
  > nand erase 0x100000 0x2000
NAND erase: device 0 offset 0x100000, size 0x2000
Erasing at 0x100000 -- 200% complete.
OK
  >
-- cut --

Correct this and give user a warning that more is erased than specified:

-- cut --
  > nand erase 0x100000 0x2000
NAND erase: device 0 offset 0x100000, size 0x2000
Warning: Erase size 0x00002000 smaller than one erase block 0x00004000
           Erasing 0x00004000 instead
Erasing at 0x100000 -- 100% complete.
OK
  >
-- cut --

Signed-off-by: Dirk Behme <dirk.behme@gmail.com>

drivers/mtd/nand/nand_util.c

@@ -153,6 +153,13 @@ int nand_erase_opts(nand_info_t *meminfo, const nand_erase_options_t *opts)
 		priv_nand->bbt = NULL;
 	}
 
+	if (erase_length < meminfo->erasesize) {
+		printf("Warning: Erase size 0x%08x smaller than one "	\
+		       "erase block 0x%08x\n",erase_length, meminfo->erasesize);
+		printf("         Erasing 0x%08x instead\n", meminfo->erasesize);
+		erase_length = meminfo->erasesize;
+	}
+
 	for (;
 	     erase.addr < opts->offset + erase_length;
 	     erase.addr += meminfo->erasesize) {