sdhci: don't assign mmc->caps at SDHCI directly

Some host controllers can set mmc->caps before sdhci_add_host().

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