mtd: nand: Fix nand write error with bad block addresses above 32-bit

Nand writes should skip the bad blocks with "nand write" command.
In case of bad blocks with above 32-bit address, nand_block_isbad()
returns false due to truncated bad block address.

In below code segment,

	if (nand_block_isbad(mtd, offset & ~(mtd->erasesize - 1)))

offset is 64-bit and mtd->erasesize is 32-bit, hence the truncation is
happening. Cast 'mtd->erasesize' with loff_t to fix this issue.

Signed-off-by: T Karthik Reddy <t.karthik.reddy@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>