drivers/nfc/pn544.c: fix min_t warnings

Fix these:

drivers/nfc/pn544.c: In function 'pn544_read':
drivers/nfc/pn544.c:356: warning: comparison of distinct pointer types lacks a cast
drivers/nfc/pn544.c:377: warning: comparison of distinct pointer types lacks a cast
drivers/nfc/pn544.c: In function 'pn544_write':
drivers/nfc/pn544.c:463: warning: comparison of distinct pointer types lacks a cast
drivers/nfc/pn544.c:485: warning: comparison of distinct pointer types lacks a cast

Cc: "Matti J. Aaltonen" <[e-mail]>
Cc: Stephen Rothwell <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/nfc/pn544.c

···
 	struct mutex read_mutex; /* Serialize read_irq access */
 	struct mutex mutex; /* Serialize info struct access */
 	u8 *buf;
-	unsigned int buflen;
+	size_t buflen;
 };
 
 static const char reg_vdd_io[]	= "Vdd_IO";