mmc: sdhci-pltfm: drop error message for too small MMIO resource size

The requirement resource_size >= 0x100 may not necessarily be
reasonable; for example, sdhci-dove appears to sidestep some
registers in sdhci_dove_readw().

Moreover, current code displays an error message for too small
resource size, but still moves forward.

Every DT should be responsible for describing its properties
correctly, so lets's remove this error message from the common
framework.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>