mmc: sdhci: Fix a potential uninitialized variable

Smatch complains that "ret" can be used without being initialized.

drivers/mmc/host/sdhci.c
  4383          if (!IS_ERR(mmc->supply.vqmmc)) {
  4384                  if (enable_vqmmc) {
                            ^^^^^^^^^^^^
  4385                          ret = regulator_enable(mmc->supply.vqmmc);
                                ^^^^^
  4386                          host->sdhci_core_to_disable_vqmmc = !ret;
  4387                  }

"ret" is only initialized when "enable_vqmmc" is true.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/20200714141410.GB314989@mwanda
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>