sparc64: Fix prototype warnings for floppy_64.h

sparc64: Fix prototype warnings for floppy_64.h

Fix the following warnings:

arch/sparc/include/asm/floppy_64.h:200:13: warning: no previous prototype for ‘sparc_floppy_irq’
arch/sparc/include/asm/floppy_64.h:437:6: warning: no previous prototype for ‘sun_pci_fd_dma_callback’

Both sparc_floppy_irq and sun_pci_fd_dma_callback are only used within
arch/sparc/include/asm/floppy_64.h that is included only by
drivers/block/floppy.c, so declare them static.

Link: https://lore.kernel.org/r/20240710094155.458731-2-andreas@gaisler.com
Signed-off-by: Andreas Larsson <andreas@gaisler.com>