mfd: ti_am335x_tscadc: Delete superfluous error message

In the function ti_tscadc_probe(), when get irq failed,
platform_get_irq() logs an error message, so remove
redundant message here.

Signed-off-by: Tang Bin <tangbin@cmss.chinamobile.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>