spi: spi-cadence-quadspi: Plug the leak of 'read_data'

In cqspi_phy_check_pattern() we allocate the array 'read_data' to read
the PHY pattern from the flash. It is not freed on return, resulting in
a leak of up to a couple kilobytes. Plug the leak.

Fixes: 5ee294ff ("spi: cadence-qspi: Tune PHY to allow running at higher frequencies")
Signed-off-by: Pratyush Yadav <p.yadav@ti.com>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>