samples: drivers: spi_flash: Add nordic,qspi-nor to test filter

When commit 5b4f4253 introduced
"nordic,qspi-nor" dts binding the sample wasn't aligned to the change.
From that moment the sample started to be filtered out by the Twister.

The patch adds Nordic's compatible to the test filter.

Signed-off-by: Adam Wojasinski <adam.wojasinski@nordicsemi.no>