dmaengine: bcm2835: fix 64-bit warning

When building this driver on arm64, we get a harmless type
mismatch warning:

drivers/dma/bcm2835-dma.c: In function 'bcm2835_dma_fill_cb_chain_with_sg':
include/linux/kernel.h:743:17: warning: comparison of distinct pointer types lacks a cast
  (void) (&_min1 == &_min2);  \
                 ^
drivers/dma/bcm2835-dma.c:409:21: note: in expansion of macro 'min'
    cb->cb->length = min(len, max_len);

This changes the type of the 'len' variable to size_t, which
avoids the problem.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: 388cc7a281 ("dmaengine: bcm2835: add slave_sg support to bcm2835-dma")
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

drivers/dma/bcm2835-dma.c

@@ -393,11 +393,12 @@ static void bcm2835_dma_fill_cb_chain_with_sg(
 	unsigned int sg_len)
 {
 	struct bcm2835_chan *c = to_bcm2835_dma_chan(chan);
-	size_t max_len = bcm2835_dma_max_frame_length(c);
-	unsigned int i, len;
+	size_t len, max_len;
+	unsigned int i;
 	dma_addr_t addr;
 	struct scatterlist *sgent;
 
+	max_len = bcm2835_dma_max_frame_length(c);
 	for_each_sg(sgl, sgent, sg_len, i) {
 		for (addr = sg_dma_address(sgent), len = sg_dma_len(sgent);
 		     len > 0;