kernel: fix sdhci-msm build error

kernel: fix sdhci-msm build error

A missing upstream stable backport leads to the following build error:

     CC      drivers/mmc/host/sdhci-msm.o
    drivers/mmc/host/sdhci-msm.c:1158:3: error: 'const struct sdhci_ops' has no member named 'write_w'
      .write_w = sdhci_msm_write_w,
       ^~~~~~~
    drivers/mmc/host/sdhci-msm.c:1158:13: warning: excess elements in struct initializer
      .write_w = sdhci_msm_write_w,
                 ^~~~~~~~~~~~~~~~~
    drivers/mmc/host/sdhci-msm.c:1158:13: note: (near initialization for 'sdhci_msm_ops')
    scripts/Makefile.build:326: recipe for target 'drivers/mmc/host/sdhci-msm.o' failed

Solve the issue by backporting commit
99d570da30 ("mmc: Kconfig: Enable CONFIG_MMC_SDHCI_IO_ACCESSORS")
from linux-stable.

Ref: https://github.com/openwrt/openwrt/commit/528508ae8b33c76deaf18f313973144a7e920678#commitcomment-32049231
Fixes: 528508ae8b ("kernel: bump 4.14 to 4.14.95")
Signed-off-by: Jo-Philipp Wich <jo@mein.io>