block: Drop some superfluous casts from void *

block: Drop some superfluous casts from void *

They clutter the code.  Unfortunately, I can't figure out how to make
Coccinelle drop all of them, so I have to settle for common special
cases:

    @@
    type T;
    T *pt;
    void *pv;
    @@
    - pt = (T *)pv;
    + pt = pv;
    @@
    type T;
    @@
    - (T *)
      (\(g_malloc\|g_malloc0\|g_realloc\|g_new\|g_new0\|g_renew\|
	 g_try_malloc\|g_try_malloc0\|g_try_realloc\|
	 g_try_new\|g_try_new0\|g_try_renew\)(...))

Topped off with minor manual style cleanups.

Signed-off-by: Markus Armbruster <[email protected]>
Reviewed-by: Max Reitz <[email protected]>
Reviewed-by: Jeff Cody <[email protected]>
Signed-off-by: Kevin Wolf <[email protected]>