fix(ufs): don't zero out the write buffer

Previously ufs_write_blocks was memsetting the write buffer before
calling ufs_prepare_cmd, causing zeros to be written to UFS. This change
deletes the memset call so the original buffer contents get written to
UFS.

Signed-off-by: Jorge Troncoso <jatron@google.com>
Change-Id: I3299f11b30e6d7d409408ce11a6759c88607ee18

drivers/ufs/ufs.c

@@ -726,7 +726,6 @@ size_t ufs_write_blocks(int lun, int lba, const uintptr_t buf, size_t size)
 	       (ufs_params.desc_base != 0) &&
 	       (ufs_params.desc_size >= UFS_DESC_SIZE));
 
-	memset((void *)buf, 0, size);
 	get_utrd(&utrd);
 	ufs_prepare_cmd(&utrd, CDBCMD_WRITE_10, lun, lba, buf, size);
 	ufs_send_request(utrd.task_tag);