[nrf fromlist] drivers: nrfwifi: WAR for performance regression

With the newly introduced settling time for PLLS, we are seeing a peak
performance drop of 3Mbps in Zperf benchmarks, and also other
performance tests are also impacted.

This settling time was introduced based on observations in lab and not
because of any real problem or bug reported, so, for now, use zero
settling time (same as earlier) till we fully investigate and understand
the impacts and need.

Fixes #80951.

Upstream PR #: 80952

Signed-off-by: Chaitanya Tata <[email protected]>
(cherry picked from commit d9bec06)

Author: krish2718

drivers/wifi/nrfwifi/src/qspi/src/qspi_if.c

@@ -125,7 +125,10 @@ BUILD_ASSERT(QSPI_IF_DEVICE_FREQUENCY >= (NRF_QSPI_BASE_CLOCK_FREQ / 16),
  * starts. It was measured with a logic analyzer (unfortunately, the nRF5340
  * specification does not provide any numbers in this regard).
  */
-#define BASE_CLOCK_SWITCH_DELAY_US 7
+/* FIXME: This has adverse impact on performance, ~3Mbps, so, for now, it is
+ * disabled till further investigation.
+ */
+#define BASE_CLOCK_SWITCH_DELAY_US 0
 
 #else
 /*