mfd: ab8500-debugfs: Fix incompatible types in comparison expression issue

Smatch reports:

 drivers/mfd/ab8500-debugfs.c:1804:20: error: incompatible types in comparison expression (different type sizes):
 drivers/mfd/ab8500-debugfs.c:1804:20:    unsigned int *
 drivers/mfd/ab8500-debugfs.c:1804:20:    unsigned long *

This is due to mixed types being compared in a min() comparison.  Fix
this by treating values as signed and casting them to the same type
as the receiving variable.

Cc: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/ab8500-debugfs.c

@@ -1801,7 +1801,7 @@ static ssize_t ab8500_hwreg_write(struct file *file,
 	int buf_size, ret;
 
 	/* Get userspace string and assure termination */
-	buf_size = min(count, (sizeof(buf)-1));
+	buf_size = min((int)count, (int)(sizeof(buf)-1));
 	if (copy_from_user(buf, user_buf, buf_size))
 		return -EFAULT;
 	buf[buf_size] = 0;