mtd: spi: Set the current bank of flash to zero after doing clear bar

mtd: spi: Set the current bank of flash to zero after doing clear bar

clean_bar() function selecting bank zero but not setting the
flash current bank to zero. After erase operation, bank zero is selected
but the flash current bank is pointing to bank one. So, during
write operation, while trying to write bank one, it actually writes in
bank zero.
This patch fixed this issue by setting the current bank of flash
to zero after doing clear_bar() after erase, write and read operations.

Signed-off-by: Vipul Kumar <vipul.kumar@xilinx.com>
Signed-off-by: Siva Durga Prasad Paladugu <siva.durga.paladugu@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>