mfd: fsl-imx25: Fix check for platform_get_irq() errors

The mx25_tsadc_remove() function assumes all non-zero returns are success
but the platform_get_irq() function returns negative on error and
positive non-zero values on success.  It never returns zero, but if it
did then treat that as a success.

Fixes: 18f77393 ("mfd: fsl-imx25: Clean up irq settings during removal")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Martin Kaiser <martin@kaiser.cx>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/YvTfkbVQWYKMKS/t@kili