drivers/block/cpqarray.c: better error handling and kmalloc + memset conversion to k[cz]alloc

This patch removes some redundant casts, does the kmalloc + memset to
k[cz]alloc conversion and it changes the error path to use goto (to avoid code
duplication).

 drivers/block/cpqarray.c | 49567 -> 48623 (-944 bytes)
 drivers/block/cpqarray.o | 178820 -> 178288 (-532 bytes)

Signed-off-by: Mariusz Kozlowski <m.kozlowski@tuxland.pl>
Acked-by: Mike Miller <mike.miller@hp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>