spi: cadence-quadspi: Silence shiftTooManyBitsSigned warning

spi: cadence-quadspi: Silence shiftTooManyBitsSigned warning

drivers/spi/spi-cadence-quadspi.c:267:18: warning: Shifting signed 32-bit
value by 31 bits is undefined behaviour [shiftTooManyBitsSigned]
    return reg & (1 << CQSPI_REG_CONFIG_IDLE_LSB);
                    ^

Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Jay Fang <f.fangjian@huawei.com>
Link: https://lore.kernel.org/r/1614854872-8694-1-git-send-email-f.fangjian@huawei.com
Signed-off-by: Mark Brown <broonie@kernel.org>