wimax/iwmc3200: don't disable the SDIO function if enable fails

In the iwmc3200, disabling the WiMAX SDIO function when enable fails
would possibly result in a device reset triggered by the iwmc3200's
top controller since it monitors the bus reset activities from each
SDIO function. In any case, the disable makes no sense; if the enable
fails, it should not be disabled.

Thus we remove the unecessary sdio_disable_func() in
i2400ms_enable_function().

Signed-off-by: Cindy H Kao <cindy.h.kao@intel.com>
Signed-off-by: Inaky Perez-Gonzalez <inaky@linux.intel.com>