Staging: zram: fix build errors, depends on BLOCK

Fix 49 zram build errors in one swoop.  Examples:

drivers/staging/zram/zram_drv.c:225: error: dereferencing pointer to incomplete type
drivers/staging/zram/zram_drv.c:226: error: implicit declaration of function 'bio_for_each_segment'
drivers/staging/zram/zram_drv.c:226: error: expected ';' before '{' token
drivers/staging/zram/zram_drv.c:281: error: implicit declaration of function 'bio_endio'
drivers/staging/zram/zram_drv.c:285: error: implicit declaration of function 'bio_io_error'
drivers/staging/zram/zram_drv.c:545: error: implicit declaration of function 'set_capacity'
drivers/staging/zram/zram_drv.c:548: error: implicit declaration of function 'queue_flag_set_unlocked'
drivers/staging/zram/zram_drv.c:548: error: 'QUEUE_FLAG_NONROT' undeclared (first use in this function)
drivers/staging/zram/zram_drv.c:548: error: dereferencing pointer to incomplete type

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>