hw/block: replace TABs with space

Bring the block files in line with the QEMU coding style, with spaces
for indentation. This patch partially resolves the issue 371.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/371


Signed-off-by: Yeqi Fu <fufuyqqqqqq@gmail.com>
Message-Id: <20230314095001.13801-1-fufuyqqqqqq@gmail.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>