spi: cadence_qspi: Set tshsl_ns to at least one sclk_ns

spi: cadence_qspi: Set tshsl_ns to at least one sclk_ns

tshsl_ns is the clock delay for chip select deassert. This is the delay in
master reference clocks for the length that the master mode chip select
outputs are de-asserted between transactions.

The minimum delay is always SCLK period to ensure the chip select is never
re-asserted within one SCLK period.

That is why tshsl_ns delay should be at least one sclk_ns value. If it is
less than sclk_ns, set it equal to sclk_ns.

Signed-off-by: Ashok Reddy Soma <ashok.reddy.soma@amd.com>
Signed-off-by: Venkatesh Yadav Abbarapu <venkatesh.abbarapu@amd.com>
Link: https://lore.kernel.org/r/20250702065717.3871435-1-venkatesh.abbarapu@amd.com
Signed-off-by: Michal Simek <michal.simek@amd.com>