mtd: spi-nor: Send write disable cmd after every write enable

mtd: spi-nor: Send write disable cmd after every write enable

Write enable(06h) command will be sent to a flash device to
set the write enable latch bit before every program, erase,
write command. After that write disable command (04h) needs
to be sent to clear the write enable latch.

This write_disable() is missing at the majority of the places
in the driver, add it to clear write enable latch.

Signed-off-by: Ashok Reddy Soma <ashok.reddy.soma@xilinx.com>
Signed-off-by: Venkatesh Yadav Abbarapu <venkatesh.abbarapu@amd.com>
Link: https://gist.github.com/PrasanthBabuMantena/c12f39744de188a9d08cd5ca51dc2a7b
Tested-by: Prasanth Babu Mantena <p-mantena@ti.com>