mmc: allow ext_csd revision 7

Newer d2 revisions are coming with version 7, this matches the stock
kernel too.

Change-Id: Ie64f681dc2dee0e52ba46dca55dfb310bf0eba93
Merge branch 'cm-10.1' of https://github.com/CyanogenMod/android_kernel_samsung_d2 into cm-10.1
hotplugging fix