Now that the block layer implement zone checks on revalidate,
sd_zbc_check_zones() is reduced getting the zone size and verifying the
device capacity for device with RC_BASIS=0. Be clear about this by renaming
sd_zbc_check_zones() to sd_zbc_check_capacity() and updating the function
description and comments.

Link: https://lore.kernel.org/r/20191220075823.400072-3-damien.lemoal@wdc.comSigned-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>