spi: spi-ti-qspi: fix warning

spi: spi-ti-qspi: fix warning

drivers/spi/spi-ti-qspi.c: In function ‘ti_qspi_start_transfer_one’:
drivers/spi/spi-ti-qspi.c:392:8: warning: ‘rx_wlen’ may be used uninitialized in this function [-Wmaybe-uninitialized]
  392 |     if (rx_wlen >= 32)
      |        ^
drivers/spi/spi-ti-qspi.c:318:12: note: ‘rx_wlen’ was declared here
  318 |  u8 rxlen, rx_wlen;
      |            ^~~~~~~

The warning is a false positive; it is not thrown by all compiler versions, e.g.
Red Hat Cross 9.2.1-1 but not Linaro GCC 7.5-2019.12.

Signed-off-by: Jean Pihet <jean.pihet@newoldbits.com>
Link: https://lore.kernel.org/r/20200115100700.3357-1-jean.pihet@newoldbits.com
Signed-off-by: Mark Brown <broonie@kernel.org>