mmc: sdhci-esdhc-imx: remove unused is_imx6q_usdhc

mmc: sdhci-esdhc-imx: remove unused is_imx6q_usdhc

The is_imx6q_usdhc() function is unused:

  drivers/mmc/host/sdhci-esdhc-imx.c:343:19: warning: unused function 'is_imx6q_usdhc'

Reported-by: kernel test robot <lkp@intel.com>
Fixes: f47c4bbfa283 ("mmc: sdhci-esdhc-imx: create struct esdhc_soc_data")
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Reviewed-by: Haibo Chen <haibo.chen@nxp.com>
Link: https://lore.kernel.org/r/20210601095403.236007-1-krzysztof.kozlowski@canonical.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>