sd-as3525v1: do not disable peripheral clocks in sd_enable()
(forward port of r26481 + cosmetics)
This lead to freezes under various conditons (bug report: FS#11267)
Battery life is almost not (if at all) affected:
- between 4 and 8 minutes less runtime for fuzev1
- 9 minutes less runtime for c200v2 (2 minutes difference on a 2 hours run)
Additional verifications of the runtime (including on other models) wouldn't hurt
git-svn-id: svn://svn.rockbox.org/rockbox/trunk@26512 a1c6a512-1295-4272-9138-f99709370657