sdhci: remove useless set_clock() check

When using QUIRK_NONSTANDARD_CLOCK, it checks the set_clock() function
which is not used actually.  So delete it.

Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Cc: <linux-mmc@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>