drivers/misc/ti-st: fix read fw version cmd

If the read firmware version response from the chip is split into multiple
frames of UART buffer being received by the host, the TI-ST driver as of today
is unable to put the pieces of response together unlike other responses.

Signed-off-by: Pavan Savoy <pavan_savoy@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>