spi_qsd: don't use "default" string for pin ctrl state

Use "spi_default" string instead of "default" to avoid
installing the active configuration by pin ctrl framework,
which leads to leakage current on the gpios when no slave is
using the spi bus.

Change-Id: I2385ef3a1283e4b15087a2adf3f3609623817da3
Signed-off-by: Kiran Gunda <kgunda@codeaurora.org>