mmc: sdhci: Fix override of timeout clk wrt max_busy_timeout

mmc: sdhci: Fix override of timeout clk wrt max_busy_timeout

Normally the timeout clock frequency is read from the capabilities
register.  It is also possible to set the value prior to calling
sdhci_add_host() in which case that value will override the
capabilities register value.  However that was being done after
calculating max_busy_timeout so that max_busy_timeout was being
calculated using the wrong value of timeout_clk.

Fix that by moving the override before max_busy_timeout is
calculated.

The result is that the max_busy_timeout and max_discard
increase for BSW devices so that, for example, the time for
mkfs.ext4 on a 64GB eMMC drops from about 1 minute 40 seconds
to about 20 seconds.

Note, in the future, the capabilities setting will be tidied up
and this override won't be used anymore.  However this fix is
needed for stable.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: stable@vger.kernel.org # v3.18+
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>