mmc: sdhci-st: Handle interconnect clock

Some ST platforms contain interconnect (ICN) clocks which must be handed
correctly in order to obtain full functionality of a given IP.  In this
case, if the ICN clocks are not handled properly by the ST SDHCI driver
MMC will break and the following output can be observed:

    [   13.916949] mmc0: Timeout waiting for hardware interrupt.
    [   13.922349] sdhci: =========== REGISTER DUMP (mmc0)===========
    [   13.928175] sdhci: Sys addr: 0x00000000 | Version:  0x00001002
    [   13.933999] sdhci: Blk size: 0x00007040 | Blk cnt:  0x00000001
    [   13.939825] sdhci: Argument: 0x00fffff0 | Trn mode: 0x00000013
    [   13.945650] sdhci: Present:  0x1fff0206 | Host ctl: 0x00000011
    [   13.951475] sdhci: Power:    0x0000000f | Blk gap:  0x00000080
    [   13.957300] sdhci: Wake-up:  0x00000000 | Clock:    0x00003f07
    [   13.963126] sdhci: Timeout:  0x00000004 | Int stat: 0x00000000
    [   13.968952] sdhci: Int enab: 0x02ff008b | Sig enab: 0x02ff008b
    [   13.974777] sdhci: AC12 err: 0x00000000 | Slot int: 0x00000000
    [   13.980602] sdhci: Caps:     0x21ed3281 | Caps_1:   0x00000000
    [   13.986428] sdhci: Cmd:      0x0000063a | Max curr: 0x00000000
    [   13.992252] sdhci: Host ctl2: 0x00000000
    [   13.996166] sdhci: ADMA Err: 0x00000000 | ADMA Ptr: 0x7c048200
    [   14.001990] sdhci: ===========================================
    [   14.009802] mmc0: Got data interrupt 0x02000000 even though no data operation was in progress.

A decent point was raised about minimising the use of a local variable that
we 'could' do without.  I've chosen consistency over the possibility of
reducing the local variable count by 1.  Thinking that it's more important
for the code to be grouped and authoured in a similar manner/style for
greater maintainability/readability.

Cc: stable@vger.kernel.org
Tested-by: Peter Griffin <peter.griffin@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>