mtd: nand_bcm: fix hot spin and code duplication

In the branch where pagesize equalled NAND_DATA_ACCESS_SIZE, NumToRead
wasn't decremented in the `while (numToRead > 11)' loop.
Also the first and last while loops were duplicated in both branches.

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Acked-by: Leo Chen <leochen@broadcom.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>