sysv: use BUILD_BUG_ON instead of runtime check

There were runtime checks about sizes of struct v7_super_block and struct
sysv_inode.  If one of these checks fail the kernel will panic.  Since
these values are known at compile time let's use BUILD_BUG_ON(), because
it's a standard mechanism for validation checking at build time

Link: https://lkml.kernel.org/r/20210813123020.22971-1-paskripkin@gmail.com
Fixes: 1da177e4

 ("Linux-2.6.12-rc2")
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>