mtd: maps: sun_uflash: Declare uflash_devinit static

This fixes the following warning:
sun_uflash.c:50:5: error: no previous prototype for 'uflash_devinit'

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Fixes: 0fcb7085 ("Makefile.extrawarn: turn on missing-prototypes globally")
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Tested-by: Randy Dunlap <rdunlap@infradead.org> # build-tested
Cc: Andreas Larsson <andreas@gaisler.com>
Cc: "David S. Miller" <davem@davemloft.net>
Reviewed-by: Andreas Larsson <andreas@gaisler.com>
Acked-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Andreas Larsson <andreas@gaisler.com>
Link: https://lore.kernel.org/r/20240224-sam-fix-sparc32-all-builds-v2-3-1f186603c5c4@ravnborg.org