USB: android gadget: mass_storage: read/write performance enhancement

As per the mass storage protocol, csw is sent from the device
after successfully writing the data on to storage media, where
there is a time factor involved. With this csw hack, csw is sent
just after receiving the data & before writing the data on the
storage media. By, any chance, if the write fails, the corresponding
lun is removed to indicate the user of write failure.

Buffers has been increased to 4, so that there is enough space for
the incoming data, which is usually 64KB per CBW.

Change-Id: I59dd9add13d1224f09d94e951ad9190c44c4d1b7
Signed-off-by: Chiranjeevi Velempati <cvelempa@codeaurora.org>
Signed-off-by: Azhar Shaikh <azhars@codeaurora.org>