[PATCH] MTD: m25p80: fix printk format warning

Fix printk format warning:
drivers/mtd/devices/m25p80.c:189: warning: format '%zd' expects type
'signed size_t', but argument 6 has type 'u_int32_t'

Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>