sf: bar: Clean BA24 Bank Address Register bit after read/write/erase operation

The content of Bank Address Register (BAR) is volatile. It is cleared
after power cycle or reset command (RESET F0h).

Some memories (like e.g. s25fl256s) use it to access memory larger than
0x1000000 (16 MiB).

The problem shows up when one:

1. Reads/writes/erases memory > 16 MiB
2. Calls "reset" u-boot command (which is not causing BAR to be cleared)

In the above scenario, the SoC ROM sends 0x000000 address to read SPL.
Unfortunately, the BA24 bit is still set and hence it receives content
from 0x1000000 (16 MiB) memory address.
As a result the SoC aborts and we hang. Only power cycle can take the
SoC out of this state.

How to reproduce/test:

sf probe; sf erase 0x1200000 0x800000; reset
sf probe; sf erase 0x1200000 0x800000; sf write 0x11000000 0x1200000 0x800000; reset
sf probe; sf read 0x11000000 0x1200000 0x800000; reset

Signed-off-by: Lukasz Majewski <lukma@denx.de>
[Fixed comment text on clean_bar function]
Signed-off-by: Jagan Teki <jagan@openedev.com>
Reviewed-by: Jagan Teki <jagan@openedev.com>