mtd: m25p80: Fix the incorrect ear value on startup

The current implementation always assume that the ear/bank register
value is always zero on startup and this would cause issue if the u-boot
which launches linux might have set it to any arbitrary value. When this
happens all initial accesses to bank 0 will return incorrect data from
the wrong bank.
On startup, this fix ensure that the curbank field is updated with the
ear/bank register value and avoid accessing the wrong bank data.

Signed-off-by: Punnaiah Choudary Kalluri <punnaia@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>