spi: spi-mem: avoid mutating op template in spi_mem_supports_op()

spi: spi-mem: avoid mutating op template in spi_mem_supports_op()

spi_mem_supports_op() accepts a const struct spi_mem_op pointer but
casts away const internally to call spi_mem_adjust_op_freq(). This
mutates the caller's op template, which causes stale max_freq values
when callers reuse persistent templates - subsequent calls won't
re-apply the device frequency cap since spi_mem_adjust_op_freq()
skips non-zero values.

Fix by operating on a stack-local copy instead.

Fixes: a4f8e70d75dd ("spi: spi-mem: add spi_mem_adjust_op_freq() in spi_mem_supports_op()")
Cc: Tianyu Xu <xtydtc@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Santhosh Kumar K <s-k6@ti.com>
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://patch.msgid.link/20260527173736.2243004-1-s-k6@ti.com
Signed-off-by: Mark Brown <broonie@kernel.org>