ide-floppy: add more debugging to idefloppy_pc_intr()

Add more debugging to idefloppy_pc_intr() to match ide-tape's
idetape_pc_intr().

While at it:

* Correct the first debug message.

* Log device name with "DMA finished" message.

This is a preparation for adding generic ide_pc_intr() helper.

Cc: Borislav Petkov <petkovbb@gmail.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>